2005 PAST MEETS PRESENT IN Astronomy and

Astrophysics PROCEEDINGS OF THE 15TH PORTUGUESE NATIONAL MEETING

EDITORS JOSE AFONSO NUNO SANTOS ANDRE MOITINHO RUI AGOSTINHO www.Ebook777.com

2005 PAST MEETS PRESENT IN Astronomy and

Astrophysics PROCEEDINGS OF THE 15TH PORTUGUESE NATIONAL MEETING

www.Ebook777.com

www.Ebook777.com

EDITORS JOSE AFONSO NUNO SANTOS ANDRE MOITINHO RUI AGOSTINHO

UNIVERSITY OF LISBON, PORTUGAL

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V °-*2005 (P PAST MEETS PRESENT IN

Astronomy and Astrophysics

PROCEEDINGS OF THE 15TH PORTUGUESE NATIONAL MEETING

UNIVERSITY OF LISBON ft LISBON ASTRONOMICAL OBSERVATORY

28 - 30 JULY 2005

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2005: PAST MEETS PRESENT IN ASTRONOMY AND ASTROPHYSICS Proceedings of the 15th Portuguese National Meeting

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FOREWORD

With a first appearance in 1991, the Portuguese National Meetings of Astronomy and Astrophysics (ENAA) are annual events that gather the astrophysics community in order to share the results of its research work.

More recently, the creation of the Portuguese Astronomical Society (SPA) has stimulated and brought new dynamics to the ENAA. This is also the result of a young and growing astronomical community, active at the forefront of current astrophysical research, as well as to the ever stronger connections with ESO and ESA.

Between the 28th and the 30th of July, 2005, the XV ENAA gathered over 80 researchers in the Faculty of Sciences of the University of Lisbon and in the Astronomical Observatory of Lisbon (OAL), to discuss the most recent findings. For the second year running, and in collaboration with the Center for the History of Sciences of the University of Lisbon, attention was also devoted to the History of Astronomy, with contributions that stress the rich past of Portuguese Astronomy. This provided a particularly attractive merger between the old and the new, between the richness, diversity and frequently unknown past of Portuguese Astronomy and the current fast-moving research.

The present ENAA was organised by the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL) and the Portuguese Astronomical Society (SPA). The programme was defined with the help of the Scientific and Local Organizing Committee: Jose Afonso (OAL/CAAUL), Nuno Santos (CAAUL), Andre Moitinho (CAAUL), Rui Agostinho (FCUL/CAAUL), Carlos Santos (CAAUL), Pedro Raposo (OAL) and Eugenia Carvalho (OAL).

The meeting was made possible by the support of a number of entities: the Faculty of Sciences of the University of Lisbon, the Astronomical Observatory of Lisbon, the Foundation for Science and Technology (Portugal), Banco Espirito Santo and Delta Cafes.

v

VI

Finally, we thank the participants for their active contribution to the success of this venture. This book is made for them, and by them.

Jose Afonso, Nuno Santos, Andre Moitinho and Rui Agostinho

Organisation:

i O K H K . l 'KSA l O L O A D t

ASTRONOMIA

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BANCO ESPIRITO SANTO

CONTENTS

Foreword v

Modern Astrophysics

Evolution of the spin of Mercury and its capture into the 3/2 spin-orbit resonance

A. CM. Correia andJ. Laskar 1

Trans-Neptunian Objects and Associated Families: confronting colors, correlations and evolution models

N. Peixinho 5

The origin of the spins of Kuiper Belt objects P. Lacerda, C. Dominik, J. Luu and S. Kenyon 9

Magnetic Turbulence in the solar wind and the earth's plasma sheet

I. Dorotovic and Z. Voros 13

The structure revealed by Spitzer in NGC 2264 P. S. Teixeira, C. J. Lada, M. Marengo, A. Muench, S. T. Megeath, G. Fazio, E. T. Young, J. Muzerolle, N. Siegler, G. Reike and L. Hartmann 17

Recent Results on Interstellar Turbulence M. A. de Avillez and D. Breitschwerdt 19

Asteroseismology and Variability of Young Stars F. J. G. Pinheiro 23

On the problem of magnetic braking J. M. Ferreira, A. Aibeo and J. Lima 27

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A first step for Automatic Stellar Parameter Determination S. G. Sousa 31

Giant Transiting Planets Observations - GITPO C. Afonso 35

Probing the structure and atmospheres of extra-solar planets N. C. Santos 39

What's going on in Canis Major? A. Moitinho, G Cagarro, R. A. Vazquez, G. Baume and E. E. Giorgi 43

Study of three galaxy clusters at intermediate redshifts C. Lobo andM. S. Roos 47

Modelling the Warm Absorber in NGC 3783 with the TITAN code

A. C. Gonqalves, A. Rozanska, S. Collin, A. M. Dumont, M. Mouchet, L. Chevallier and R. W. Goosmann 51

Astrophysical Tests of Fundamental Physics C. J. A. P. Martins 55

Gamma Ray Bursts as Cosmological Probes O. Bertolami and P. T. Silva 59

Braneworld cosmology: sneutrino inflation and leptogenesis N. M. C. Santos, M. C. Bento and R. G. Felipe 63

XCS - Current Status P.T.P. Viana 67

Deep radio observations in the CDFS/GOODS field: optical and X-ray identifications

J. Afonso 71

The nature of the optical faint sub-millijansky radio sources: the VLT/VIMOS view

D. Sobral and J. Afonso 75

IX

AMS - a magnetic spectrometer on the international space station

L. Arruda, F. Barao, G. Barreira, J. Borges, F. Carmo, P. Gongalves, R. Pereira and M. Pimenta 77

History of Astronomy

The legacy of Sacrobosco: Tractatus de Sphaera B.Almeida 79

Astronomical and Geophysical Activities in Rio de Janeiro (Brazil) during 1781-88 by Bento Sanches Dorta

J. M. Vaquero, R. M. Trigo and M. C. Gallego 83

Comparison between Monteiro da Rocha and Wilhelm Olbers' Methods for the determination of the orbits of comets

F. B. Figueiredo and Joao Fernandes 85

The 1870 Portuguese solar eclipse expedition -a preliminary report

V. H. Bonifacio, I. Malaquias and J. M. Fernandes 89

The Science Palaces J.D.C.G. Jorge 93

The astronomer/instrument maker Campos Rodrigues and the contribution of the Observatory of Lisbon for the 1900-1901 solar parallax programme

P.Raposo 97

The Astronomical Observatory of Lisbon P. M. deAbreu 101

Time Service and Legal Time in Portugal M. Silva and R. Agostinho 105

Documents of the OAL's architecture R. G. Batista andR. Agostinho 109

MODERN ASTROPHYSICS

EVOLUTION OP THE SPIN OF MERCURY A N D ITS C A P T U R E INTO THE 3 / 2 SPIN-ORBIT R E S O N A N C E

ALEXANDRE C. M. CORREIA Departamento de Fisica da Universidade de Aveiro,

Campus Universitdrio de Santiago, 3810-193 Aveiro, Portugal

J A C Q U E S L A S K A R

Astronomie et Systemes Dynamiques, IMCCE-CNRS UMR8028

77 Av. Denfert-Rochereau, 75014 Paris, France

The present spin of Mercury is very peculiar and was only discovered in 1965: the planet spins three times around its axis exactly in the same time as it completes two orbital revolutions1. The way the planet evolved into this configuration remained a mystery until very recently2. In order to understand this phenomena we must take into account the planetary perturbations over Mercury's orbit, that continuously change its eccentricity. As a result, for any initial rotation rate it was found that the chances of capture in the present configuration rise to about 55.4%.

Tidal dissipation and core-mantle friction will drive the obliquity of Mercury close to zero. For zero degree obliquity, the averaged equation for the rotational motion near the p resonance (where p is a half-integer) writes2'3:

X C

C 2 2 = —6-3 n „ f iff (p, e) sin 2(/ - PM) - 3 ^ ( f ) Q [11(e)* - N(e)] ,

where x = i/n is the ratio of the rotation rate to the mean motion n, M the mean anomaly, e the eccentricity, £ a structure constant and H(p, e) Hansen coefficients 3. Q(e) = (1 + 3e2 + 3e4 /8)/( l - e2)9/2 , JV(e) = (1 + 15e2/2 + 45e4/8 4- 5e6/16)/(l - e2)6, fc2 and Q are the second Love number and quality factor, while a, m, ma are the semi major axis, the mass of the planet, and the solar mass. The equilibrium is achieved when x = 0, that is, for a constant eccentricity e, when x = xi(e) = N(e)/Ci(e). In a circular orbit (e = 0) this equilibrium coincides with synchronization (x — 1), while the equilibrium rotation rate x = 3/2 is achieved for 63/2 = 0.284927.

1

2

For the present value of Mercury's eccentricity e « 0.206 the capture probability in the 3/2 spin-orbit resonance3 is estimated to be about 7.73%. However, using the present value of the eccentricity of Mercury is question­able, as the eccentricity suffers strong chaotic variations in time, due to planetary secular perturbations4'5. Indeed, the eccentricity of Mercury can vary from nearly zero to more than 0.45, and thus reach values higher than the critical value e3/2 = 0.284927 (Fig.l). Additional capture into resonance can then occur, at any time during the planet's history.

Figure 1. Examples of the possible variations of the eccentricity some 4 Gyr ago. All these solutions converge to the known present evolution of the planet's orbit. Traced horizontal line corresponds to the critical eccentricity e 3 / 2 = 0.2844927.

3

In order to check this scenario, it is not possible to use a single orbital solution, as due to its chaotic behavior, the motion cannot be predicted precisely beyond a few tens of millions of years. A statistical study of the past evolutions of Mercury's orbit is then performed, with the integration of 1000 orbits over 4 Gyr in the past, starting with very close initial conditions, within the uncertainty of the present ones (Fig.l). This statistical study was made possible by the use of the averaged equations for the motion of the Solar System4'5. For each of these 1000 orbital motion of Mercury, the rotational motion (Eq.l) was integrated numerically with planetary perturbations, for p = k/2;k = 1,... ,10. Simulations were started at io = —4 Gyr, with a rotation period of 20 days (x « 4.4), using £ = 0.3333, k-z = 0.4 and Q = 50. As e is not constant, x(t) will tend towards a limit value x(t) that is similar to an averaged value of xi(t) and capture into resonance can now occur more often (Fig.2).

1.8 1.7 1.6

X 1.5 1.4 1.3 1.2 1.1

0.34 0.32

>, 0.30 •5 0.28 '= 0.26 g 0.24 o 0.22 0) 0.20

0.18 0.16

-4 -3.98 -3.96 -3.94 -3.92 -3.9 time (Gyr)

Figure 2. Rotation rate for a non constant eccentricity (b). The limit solution of equation (1) is no longer x\ = N(e)/fl(e) [(a) dotted line], but now given by: x(t) = (x(0) + K f* N(e(r))g(r)dr) /g(t), where g(t) = exp(K /„' « (e ( r ) ) dr) [(a), filled line]. In this example, there is no capture at the first crossing of the 3/2 resonance (at t ss —3.9974 Gyr). About 100 Myr later, as the mean eccentricity increases, additional crossing of the 3/2 resonance occurs, leading to capture with damping of the libration.

4 -3.98 -3.96 -3.94 -3.92 -3.9

J 1 I I I I I I L

4

All the 1000 solutions were followed, starting from —4 Gyr, until they reached the present date or get captured into the 2/1, 3/2, or 1/1 reso­nances. Contrarily to previous studies, it was found that capture into the 1/1 resonance is possible, as the eccentricity of Mercury may decrease to very low values, where the capture can occur, and the resonance remains then stable. The 3/2 remains stable, except for extremely small values of the eccentricity2. Indeed, over 554 solutions that were captured into the 3/2 resonance, a single solution, initially captured at —3.995 Gyr, escaped from resonance at about —2.396 Gyr. The solution then got trapped into the 1/1 resonance at —2.290 Gyr, capture that was favored by the low ec­centricity required to destabilize the 3/2 resonance. Out of the 56 solutions initially trapped into the 2/1 resonance, 10 were destabilized and only 2 of them were further captured, one into 3/2 resonance, and one into 1/1 resonance. Globally, only 38.8% of the solutions did not end into resonance, and the final capture probability distribution was2:

Pi / i = 2.2%, P 3 / 2 = 55.4%, P 2 / 1 = 3.6% .

With the consideration of the chaotic evolution of the eccentricity of Mercury, it is then shown that with a realistic tidal dissipative model that properly accounts for the damping of the libration of the planet, the present 3/2 resonant state is the most probable outcome for this planet. The largest unknown remains the dissipation factor fo/Q in (Eq.l). A stronger dissi­pation would increase the probability of capture into the 3/2 resonance, as x{t) would follow more closely xi(e(t)) (Fig.2), while lower dissipation will slightly decrease the capture probability.

Acknowledgements This work was supported by PNP-CNRS, Paris Ob­servatory CS, and project POCTI/FNU/43656/2001, Portugal. The nu­merical computations were made at IDRIS-CNRS, and Paris Observatory.

References

1. Pettengill, G. H., and Dyce R. B., Nature 206, 1240 (1965) 2. Correia, A.C.M., and Laskar, J., Nature 429, 848 (2004) 3. Goldreich, P., and Peale, S.J., AJ 71, 425 (1966) 4. Laskar, J., Icarus 88, 266 (1990) 5. Laskar, J., A&A 287, L9 (1994)

T R A N S - N E P T U N I A N OBJECTS A N D ASSOCIATED FAMILIES: CONFRONTING COLORS, CORRELATIONS

A N D EVOLUTION MODELS.

N. PEIXINHO CAAUL, Observatorio Astrnomico de Lisboa,

Tapada da Ajuda,

1349-018, Portugal E-mail: peixinho@oal.ul.pt

LESIA, Observatoire de Paris, 5, Place Julles Janssen,

92195 Meudon Cedex, France

With the last update of the "Meudon Multicolor Survey" we now possess a data sample of visible colors for 122 objects. Through this large data set we have analyzed: a) the interrelations between the colors and orbital parameters of Trans-Neptunian Objects and associated populations; b) the "genetic" links between them; and c) the compatibility between our statistical results and the surface and dynamical evolution models for these objects.

1. Introduction

Discovered in 19921, Trans-Neptunian objects (TNOs) are a population of small icy bodies beyond the orbit of Neptune, forming the Edgeworth-Kuiper belt (EKB). Presently more than 1000 objects have been identified. TNOs are expected to be well-preserved fossil remnants of the formation of the solar system, assumed to be icy-conglomerates composed by water ice, complex molecules formed out of H, C, N, O, and dust. TNOs are usu­ally subdivided in the dynamical families: Classical objects, Scattered Disk Objects (SDOs), Plutinos and other resonants. TNOs are also the prob­able precursors of Centaurs - objects with chaotic orbits between Jupiter and Neptune - short period comets (SPCs) and irregular satellites of giant planets.

The long-term irradiation of the icy surfaces of TNOs should generate a solid crust of carbon-complex compounds with reddish colors2. Impact

5

6

collisions, however, may excavate buried unirradiated material, with bluish colors, from beneath such crust3. Moreover, sublimation of volatiles that may refreeze on the surface is also expected. The competition between these effects should generate the wide color variety currently observed among TNOs4. The knowledge of their physical and chemical properties is crucial to constrain the formation and evolution models of our solar system.

2. Observational data

TNOs are inherently faint (my ~ 22 — 23) and difficult to detect. Conse­quently, with today's instrumentation, only multicolor photometry — which provides a first-order indication of their surface composition — provides a representative analysis of TNO's surfaces. Prom two large observation pro­grams, the "ESO Large Program on Centaurs and TNOs", using NTT and VLT, and the "Meudon Multicolor Survey", using CFHT, we have obtained visible photometry for a total of 122 objects — the largest data sample an­alyzed for far.

3. Discussion

In order to understand the physical processes responsible for their color distribution we have carried out a statistical analysis of the interconnections between the colors and orbital parameters of each family. Major results are summarized below.

3.1. Color-orbital parameters' correlations

The most recent models for the solar system show that the giant planets migrated while scattering a disk of planetesimals5. As a consequence, the EKB should consist in a superposition of a low inclined ("cold") and a high inclined ("hot") population. Our sample shows a red cluster of Clas­sical TNOs at orbital inclinations i < 4.5°, in contrast with a large color dispersion at higher inclinations, supporting such dynamical models6. See Figure 1.

We also detect a color-perihelion (q) correlation among Classical TNOs, that is much stronger for objects larger than ~ 220 km6. This points to some surface alteration by cometary activity (outgassing), which is more effective for larger objects4. See Figure 2.

Other families do not evidence for physically relevant trends between colors and orbital parameters. Note, however, that due to the unstable dy-

7

namical history of these families such results cannot immediately be taken as surprising. This issue needs further studies.

1 1

—•

•—

_ p _

•—

_

H- -—•—

-•—•—

^

Classical TNOs

— 1 —

1

=«rl • fclr 1=4.5 :

I ' • ' • ' • ' ' — — J • — = - " ' 1 ' <—

0.8 1 1.2 1.4 1.6 1.8 2 2.2 (B-R) Color

Figure 1. B-R colors vs. orbital inclination for Classical objects. The separation be­tween the dynamically "hot" and the dynamically "cold" populations is clear through the cluster of red objects below 4.5°.

3.2. Comparing families'colors

To investigate for "genetic" links between TNOs and their presumable asso­ciated populations we have compared their color distributions7. Essentially all families of TNOs and Centaurs seem mutually color-compatible. How­ever, SPCs are not color-compatible with Centaurs — the transition phase between TNOs and SPCs — and are also in a borderline incompatibility with SDOs — the most probable source of Centaurs. This suggests that the "violent" cometary activity that SPCs suffer strongly modifies their surfaces8, in contrast with the slow outgassing among Centaurs and TNOs. Moreover, irregular satellites and SPCs exhibit very similar color distri­butions, pointing to a similar surface processing. Nevertheless, we should highlight that there is no clear separation between some dynamical families — which may bias our results — and our sampling is too low to clarify such issue with the aid of colors. These studies require larger samples.

2.2

2

1.8

3 1-6 h CC

S. 1.4

1.2

1

0.8

[ ]

[ ]

t [ ]

[ ]

32 34 38

Perihelion

Figure 2. B-R colors vs. perihelion for Classical objects. It is clear that the correlation for objects larger than 220 km (black squares) is stronger than for those smaller than 220 km (white squares). The line is drawn to guide the eye.

4. Con c lu s ion s

Current models seem to provide consistent explanations for some color dis­

tributions of TNOs and associated populations. Nonetheless, the lack of

t rends among certain families shows tha t the processes are much more com­

plex. Larger sampling and bet ter modeling are still needed.

A c k n o w l e d g m e n t s

N. P. acknowledges F C T funding (ref: SFRH/BD/1094/2000) .

R e f e r e n c e s

1. D. Jewitt and J. Luu, Nature 362, 730 (1993). 2. L. M. Shul'Man, IAU Symp 45, 265 (1972). 3. J. Luu and D. Jewitt, Astron. J. 112, 2310 (1996). 4. A. Delsanti, O. Hainault, E. Jourdeuil, et al., A & A 417, 1145 (2004). 5. H. F. Levison and A. Morbidelli, Nature 426, 419 (2003). 6. N. Peixinho, H. Boehnhardt, I. Belskaya, et al., Icarus 170, 153 (2004). 7. A. Doressoundiram, N. Peixinho, C. Doucet, et al., Icarus 174, 90 (2005). 8. D. Jewitt, Astron. J. 123, 1039 (2002).

THE ORIGIN OF THE SPINS OF KUIPER BELT OBJECTS

P E D R O L A C E R D A

Grupo de Astrofisica da Universidade de Coimbra

Departamento de Matemdtica, Lg. D. Birds, 3000 Coimbra, Portugal E-mail: placerda@mat.uc.pt

C A R S T E N D O M I N I K

Sterrekundig Instituut "Anton Pannekoek" Kruislaan 403, NL-1098SJ Amsterdam, Netherlands

J A N E LUU

MIT Lincoln Laboratory 244 Wood Street, Lexington, MA 02420, USA

S C O T T K E N Y O N

Smithsonian Astrophysical Observatory 60 Garden Street, Cambridge, MA 02138, USA

We have developed a simple model to study the collisional evolution of the spins of Kuiper Belt objects (KBOs). We find that the observed spins of KBOs larger than ~ 200 km cannot be explained by collisions, if the objects had no spin at the end of the primary growth phase. This suggests that large KBOs must have attained their spin rates very early in their evolution. If the accretion process was not entirely isotropic, and contributed angular momentum to the growing KBOs, we find that a ~ 10% asymmetry in the net angular momentum of accreted plan-etesimals would explain the observations. However, if the accreted planetesimals were comparable in size to the growing body, no anisotropy is required because the accretion of individual particles can produce significant spin changes.

1. Motivation

Kuiper Belt objects (KBOs1) collide on timescales smaller than the age of the solar system. Their physical and dynamical properties should there­fore show signatures of such encounters. KBOs grew by accretion2 of dust condensates in about ~ 100 Myr. This time was set by the formation of Neptune, which excited relative velocities thus averting further accretion.

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10

Table 1. Spin rates of large KBOs.

Object Designation

2003 A Z 8 4

20000 Varuna 42301 2001 URi63 55637 2002 UX 2 6

55636 2002 TX300 50000 Quaoar 28978 Ixion

2003 E L 6 i

Radius [km] 450 490 510 545 625 650 655 750

P [hr]

13.44 6.34

--

16.24 17.69

-3.9

Ref.

3 4 3 3 3 5

3,6 7

Since then collisions have been the main interaction between KBOs. If the accretion process supplied zero average torque to the growing bodies, angu­lar momentum conservation should lead to these objects having little spin by the end of the growth phase. This is different from what is observed today, where 5 out of the 8 largest KBOs (r ~ 500 km) with measured rota­tion have spin periods below 20 hr (Table 1). This has led us to investigate the effect of collisions on KBO spin rates, in the last ~ 4 Gyr.

2. The model

Our model follows one KBO at a time, as it collides with the surrounding bodies, for 4 Gyr time. The collisional environment, described by the total mass, size and velocity distributions of KBOs, determines the total number, and the character of individual collisions. Changes in the target's mass and spin rate are calculated for each individual collision, as a function of several parameters describing individual objects and the enviroment. After all col­lisions have been accounted for we register the final spin and mass of the tar­get, and can start the process all over again. By running the model several times with the same initial conditions, we obtain a Monte Carlo estimate of the distribution of spins that a particular set of parameters generates.

3. Resul ts and Discussion

The main result discussed here is that collisions did not significantly change the spins of KBOs with radii r > 200 km. The reason is that in the last ~4 Gyr, these objects did not collide with large enough projectiles to alter their spin angular momentum. Figure 1 illustrates this result: it shows the final spin rate distribution for 500 km-radius KBOs predicted by our simulations. The KBOs start with no spin. The Figure shows that if 500 km bodies have negligible spin by the end of the formation epoch, collisions would only spin them up to P ~ 300 hr after 4 Gyr. As our simulations fail to reproduce the

11

P (hr) 100 316 1000 3162 10000

60

50

40

A

| 3" a

so

10

0 2.0 2.5 3.0 3.5 4.0

logioP (hr)

Figure 1. Distribution of final spins for 250 bodies of initial radius r = 500 km.

observed spin rates, we conclude that large KBOs must have had similar spins to what they have today at the start of the collisional evolution.

4. Anisotropic accretion

A possible mechanism to spin up large KBOs during the growth phase is anisotropic accretion. To find out the amount of anisotropy required to explain the spins of the largest KBOs we simulated the growth of a body initially 5 km in radius, by accretion of smaller projectiles, until it reaches r = 500 km. Anisotropy is parameterized by (z), denned as the normalized mean angular momentum brought into the target by each projectile. The value of (z) determines the allowed projectile impact geometries: if (z) « 0 then accretion is nearly isotropic and projectiles bring no net torque, while with (z) « 1 all projectiles tend to spin the target in the same direction. The mass of each projectile is set to a constant fraction, k, of the instan­taneous mass of the growing body. The projectiles impact velocity is the escape velocity of the target, and they always adhere. This appropriately simulates the runaway accretion phase, when relative velocities are small. Figure 2 shows how the spin rate evolves as the KBO grows, for different pairs ((z), k). An equilibrium spin rate is attained very quickly in all cases, which does not depend on the initial spin rate. Fluctuations in the spin rate due to individual projectiles are considerably smaller both with increasing (z) and decreasing k. Also, the closer (z) is to 1 the faster the final spin. Values (z) ~ 0.1 would explain the spin rates shown in Table 1. The ratio of projectile mass to target mass, k, only influences the final spin of the grow-

12

14 IS 16 17 IB 19 20 21 14 15 16 17 IB 19 20 Zl 14 15 18 17 18 19 20 21 log mans (kg) log mass (kg) log mass (kg)

/^ *=10-« (s)=0.40

14 15 16 17 IB IB 20 21 14 15 16 17 16 19 20 21 14 15 16 17 18 19 20 21 log mass (kg) log mass (kg) log mass (kg)

Figure 2. Evolution of target's spin period, as it grows, for six combinations of (z) and k. Different lines correspond to target's initial spin period P RS 3.3 hr (solid), P = 9.23 hr (dotted), and no initial spin (dashed).

ing KBO for nearly isotropic accretion, i.e., if (z) « 0. Ratios k > 0.01 also

explain the measured spin periods, even under completely isotropic growth.

This corresponds to a ratio of projectile to target radius of /c1/3 « 0.2.

5 . S u m m a r y

Our main conclusions are: (1) Collisions have not changed the spins of the

largest KBOs (r > 200 km) in the last ~ 4Gyr : their present spins must

have been set by the end of the accretion phase; (2) A 10% anisotropy in the

accretion process can produce the observed spins of KBOs; (3) If the (last)

planetesimals accreted onto the large KBOs were at least 20% of the size of

the growing bodies then isotropic accretion can explain the observations.

R e f e r e n c e s

1. J. X. Luu and D. C. Jewitt, ARA&A 40, 63 (2002). 2. S. J. Kenyon and J. X. Luu, AJ118, 1101 (1999). 3. S. S. Sheppard and D. C. Jewitt, Earth Moon and Planets 92, 207 (2003) 4. D. C. Jewitt and S. S. Sheppard, AJ 123, 2110 (2002) 5. J. L. Ortiz, P. J. Gutierrez, A. Sota, V. Casanova and V. R. Teixeira, A&A

409, L13 (2003) 6. P. Lacerda and J. Luu, AJ in press (2006) 7. D. Rabinowitz, M. Brown and C. Trujillo, AJ in press (2006)

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1

*

'1 k=lV* <se>=0.10

10

MAGNETIC TURBULENCE IN THE SOLAR WIND AND THE EARTH'S PLASMA SHEET

I. DOROTOVIC

Observatorio Astronomico da Universidade de Coimbra and Grupo de Astrofisica da Universidade de Coimbra, Portugal; UNINOVA-CRI/CA3, Caparica, Portugal, Email:

id@uninova.pt; Slovak Central Observatory, Hurbanovo, Slovak Republic, Email: dorotovic@suh. sk

Z. VOROS

Space Research Institute AAS, Austria, Email: zoltan.voeroes@oeaw.ac.at

In general, if turbulence is present in MHD plasmas, it cannot be ignored. There is also evidence that the Sun is the main driver of space weather. It has already been demonstrated in our recent study that the non-Gaussian characteristics of magnetic turbulence in the solar wind and the occurrence of intermittent magnetic turbulence in the Earth's plasma sheet can be interconnected. In this respect a comparative analysis of the solar wind magnetic and plasma parameters with the time evolution of the geomagnetic indices is insufficient. Therefore, a wider statistical study which includes the consideration of intermittency parameters during several coupling events during the period of 1996 - 2002 was performed as well.

1. Introduction

It is generally accepted that nonlinear couplings and turbulence play a key role in the study of solar wind - magnetosphere interaction processes. There is also evidence that if turbulence is present in MHD plasmas, it cannot be ignored. Recent approaches to address the problem of intermittency in solar wind turbulence have been discussed e.g. in [1].

In our preliminary study ([2]), we investigated the non-Gaussian characteristics of intermittent magnetic field fluctuations available from simultaneous observations in the solar wind (SW) and in the Earth's plasma sheet (PS), and we demonstrated that the non-Gaussian characteristics of magnetic turbulence in the solar wind and the occurrence of intermittent magnetic turbulence in the Earth's plasma sheet (PS) can be reliably interconnected. In the next step ([3]) we performed a wider statistical study which includes the consideration of intermittency parameters (skewness and kurtosis) during several coupling events during the period of 1996 - 2002. We intend to publish here only a brief overview of the main results of this investigation, while details can be found in the last two cited papers.

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2. Solar wind and plasma sheet data

In these studies we used velocity (Vx) and magnetic field (Bz) measurements in the SW available from the WIND satellite ([4], [5]) and ACE spacecraft ([6], [7]). The SW measurements are compared to simultaneous measurements of velocity (Vx) and magnentic field (Bx) in the Earth's PS available from the GEOTAIL mission. We selected only those events when the satellite was in GSM positions X e (-15 •*• -25) RE, Ye (-10 -*- 10) RE, and, moreover, when the I Bx\ < 15 nT, to ensure that the GEOTAIL was in the PS during the selected events. Based on these selection criteria, we identified 38 suitable events (with a different duration from 6 to -18 hours). All the data from GEOTAIL, Wind and ACE for the selected events during the period of 1996-2002 were obtained from the web site http://rumba.gsfc.nasa.gov/cdaweb/. Further details on input data can be found in [2] and [3].

3. Non-Gaussian intermittent fluctuations in SW and PS interaction processes

To be able to evaluate the statistics of magnetic fluctuations at different time scales, we usually consider two-point differences defined by Equation 2.1 in the paper [1]:

KB=B{t+c)-B{c) (1)

Then we constructed the so-called probability distribution functions (PDFs) for two ranges of time scales: x = 15, 30,. . . , 120 s (taul), and x = 540, 555,.. . , 645 s (tau2), respectively. The scale-dependent changes in the shape of PDFs represent a measure of intermittent character of turbulent plasma flows. The flows are more intermittent when the peakedness of PDFs grows towards small scales [3]). The main aim of our investigation referred in [3] was to perform statistical study of skewness (s) and kurtosis (k) estimated for individual events. In order to study the effect of solar wind turbulence on plasma sheet fluctuations, scatterplots ofs and k were constructed in both regions [3].

4. Conclusions

Based on these studies ([2], [3]), we can conclude that: stronger interconnection of SW and PS occurs at smaller time scales (taul), larger values of the kurtosis occur in the magnetotail when the corresponding kurtosis is also larger in the SW,

15

All these facts indicate that coupling mechanisms between the solar wind and Earth's magnetosphere might be stronger during the intervals when turbulence is present in the SW.

Acknowledgments

The authors are grateful to N. Ness and D.J. McComas for providing ACE data, R. Lepping and K.W. Ogilvie for providing Wind, and S. Kokubun and L. Frank for the GEOTAIL data. This work has been supported by FCT (MCES, Lisbon, Portugal) grants SFRH/BPD/14628/2003, and partially POCTI-SFA-2-675 (I.D.).

References

1. Voros, Z., Leubner, M. P., and Baumjohann, W.: 2005, Cross-scale coupling induced intermittency near interplanetary shocks, J. Geophys. Res., in press.

2. Dorotovid, I., and Voros, Z.: 2004, in Multi-Wavelength Investigations of Solar Activity, Proceedings IAU Symposium No. 223, eds. A.V. Stepanov, E.E. Benevolenskaya and A.G.Kosovichev, 537, DOI: 10.1017/S1743921304006763.

3. Dorotovic, I. and Voros Z.: On the Earth's plasma sheet response to the magnetic turbulence in the solar wind, in Proceedings of the 11th European Solar Physics Meeting: The Dynamic Sun: Challenges for Theory and Observations, Leuven, Belgium, September 11-16, 2005, ESA SP-600, ed. D. Danesy, in press.

4. Ogilvie K. W., et al.: 1995, Space Sci. Rev., 71, 55. 5. Lepping, R. P., et al.: 1995, in The Global Geospace Mission, ed. by C. T.

Russell, Kluwer, 207. 6. McComas, D. J., Bame, S. J., Barker, P., Feldman, W. C, Phillips, J. L.,

Riley, P., Griffee, J. W.: 1998, Space Sci. Rev., 86, 563. 7. Smith, C. W., L'Heureux, J. L., Ness, N.F., Acuna, M. H., Burlaga, L. F.,

and Scheifele, J.: 1998, Space Sci. Rev., 86, 613.

T H E S T R U C T U R E R E V E A L E D B Y SPITZER I N N G C 2 2 6 4

P. S. TEIXEIRA** C. J. LADA, M. MARENGO, A. MUENCH, S. T.

MEGEATH, AND G. FAZIO

Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Mail Stop 72, Cambridge, MA 02138, USA

Email: pteixeira@cfa.harvard.edu

E. T. YOUNG, J. MUZEROLLE, N. SIEGLER, AND G. REIKE

Steward Observatory, University of Arizona 933 North Cherry Avenue, Tucson, AZ 85721, USA

L. HARTMANN

Dept. Astronomy, University of Michigan 500 Church St., 830 Dennison Building, Ann Arbor, MI 48109, USA

We present initial results on a very young and highly embedded region of NGC 2264. The 24fj,m sources detected are found to be mostly protostellar and spatially located in linear patterns that coincide with dense filaments of molecular material. Furthermore, their quasi-regular separations is consistent with the value for the Jeans length in the region, indicating that the filaments have thernally fragmented and we are observing the primordial substructure of the cluster.

1. I n t r o d u c t i o n

NGC 2264 is cluster tha t has been very well studied 5 and known as an

active star-forming region 1,6>2. We present results on one of the youngest

regions within NGC 2264, IRS-2, observed in the submillimeter6 and in the

millimeter3 . This paper presents results obtained by observing NGC 2264

with the Spitzer Space Telescope in the following wavelengths: 3.6, 4.5, 5.8,

8, 24, 70, and 160/xm.

* University of Lisbon, Portugal tWork sponsored by the graduate fellowship SFRH/BD/13984/2003 of the Fundagao para a Ciencia e Tecnologia, Portugal

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18

n g u r e JL. (jrey scaie image 01 one 01 ine youngesi regions m i\HjUis;«>4, 1H.B-Z. l n e bright saturated source corresponds to IRAS 06382+0930, the wispy nebulosity corre­sponds to polycyclic aromatic hydrocarbon (PAH) emission. The image shows particular linear alignments of bright sources.

2. Analysis and Discussion

The 24/i4m sources are found to be mostly protostars (~60% are Class I sources). These sources are additionally found to be aligned in linear patterns that seem to point back at IRAS 06832+0930, and these chains of protostars are coincident with dense dusty filaments of molecular material 6 '3. The main results obtained are that the bright 24 /an sources are tracing the primordial substructure of the cluster, and that the molecular filaments have thermally fragmented since we observe that the spacing between the protostars is regular and consistent with the Jeans length for that region 4.

References

1. M. Margulis, C. J. Lada, and R. L. Snell, ApJ, 333, 316 (1988). 2. B. Reipurth, K. Yu, G. Moriarty-Schieven, J. Bally, C. Aspin, and S. Heath-

cote, A J, 127, 1069 (2004). 3. N. Peretto, P. Andre, and A. Belloche, A&A, in press (2005). 4. P. S. Teixeira, C. J. Lada, E. T. Young, M. Marengo, A. Muench, J. Muzerolle,

N. Siegler, G. Rieke, L. Hartmann, S. T. Megeath, and G. Fazio, ApJ, in press (2005).

5. M. F. Walker, A J, 59, 333 (1954). 6. G. Wolf-Chase, G. Moriarty, Schieven, M. Fich, and M. Barsony, MNRAS,

344, 809 (2003).

RECENT RESULTS ON INTERSTELLAR TURBULENCE

M. A. D E AVILLEZ 1 ' 2 A N D D. B R E I T S C H W E R D T 2

Department of Mathematics, University of Evora, Portugal Institut fur Astronomie, Universitat Wien, Austria E-mail: mavillez,breitschwerdt@astro.univie.ac.at

The statistical properties of interstellar turbulence are studied by means of three-dimensional high-resolution HD and MHD simulations of a SN-driven ISM. It is found that the longitudinal and transverse turbulent length scales have time aver­aged (over a period of 50 Myr) ratios of 0.5-0.6, almost similar to the one expected for isotropic homogeneous turbulence. The mean characteristic size of the larger eddies is found to be ~ 75 pc. Furthermore, the scalings of the structure functions measured in the simulated disk show unambiguous departure from the Kolmogorv (1941) model being consistent with the latest intermittency studies of supersonic turbulence (Politano & Pouquet 1995; Boldyrev 2002). Our results are indepen­dent of resolution, indicating that convergence has been reached, and that the unresolved smaller dissipative scales do not feed back on the larger ones.

1. Introduction

Interstellar turbulence is mainly driven by the energy injected into the ISM by supernovae, with the driving scale still being uncertain. It is also unclear what the statistical properties of the turbulent interstellar gas are, if the full available range of energies is taken into account. In this paper we discuss the statistical properties of the interstellar turbulence in the Galactic disk based on three-dimensional adaptive mesh refinement (AMR) simulations of the ISM, which include the disk-halo-disk circulation f1]. In particular we explore the injection scales (section 2) and the scalings of the velocity structure functions (section 3) of the interstellar turbulent gas and discuss (section 4) their implications.

2. The injection scale of interstellar turbulence

The outer scale of the turbulent flow in the ISM is related to the scale at which the energy in blast waves is transferred to the interstellar gas. Such a scale can be determined by means of the longitudinal and transversal correlation lengths, L\\ and Lkk, respectively. Here, k = 2,3 refer to

19

20

the directions perpendicular to the 1-direction along which the correlation lengths are calculated. For isotropic turbulence Lkk = 0.5Ln. Figure 1 shows the history of i n (left panel) and L22/L11 (right panel) during 50 Myr of evolution of the unmagnetized and magnetized ISM. For details on how i n and L22 are calculated see [6]. Although (£11 )t ~ 75 pc, the scatter of L\\ around its mean results from the oscillations in the local star formation rate, where the formation and merging of superbubbles, is responsible for the peaks observed in the two plots. The similarity between the average HD and MHD injection scales is due to the fact that magnetic pressure and tension forces cannot prevent break-up as long as L < /3pA, where L and A are the scale lengths of thermal and magnetic pressures (including tension forces) and ftp = A-KP/B2 is the plasma beta.

3*50 360 370 380 390 400 350 360 370 3S0 390 400 i [Myr] I [Myr!

Figure 1. History of the characteristic size (given by L\\) of the larger eddies (left panel) and of the ratio L22/LW (right panel) for the HD (dashed line) and MHD (solid line) runs.

Despite the large scatter seen in L22/L11, the time average ( Z ^ / i n ) * over the 50 Myr period is 0.51 and 0.6 for the HD and MHD runs, re­spectively. The discrepancy from 0.5 by about 20% in the MHD case is a consequence of the anisotropy introduced by the field into the flow. The (L22/Lu)t ~ 0.5 in the HD run indicates that in a statistical sense the interstellar unmagnetized turbulence is roughly isotropic.

3. Scalings of the Structure Functions

The statistics of turbulent flows in physical space is commonly characterized by the velocity structure functions of order p defined as Sp(l) = (|AV/|P), with AVi = v(x + l) —v(x), where v(x + l) and v(x) are the velocities along the a;—axis at two points separated by a distance I, such 77 <C £ <C L, L be­ing the energy integral scale and r\ the Kolmogorov scale, respectively. For homogeneous and isotropic turbulence, the Kolmogorov (K41) [2] theory

21

predicts that (|A1^|3) = - § d for / » z/3/4e -1/4 . Here, v is the kinematic viscosity and ( ) stands for average over the probability density function of AV(Z). As a consequence of this relation, within the inertial range one can write (|AV|P) oc ( |Ay| )^(p\ Experiments show that this expression, with the same scaling exponents, is valid in a wide range of length scales for large as well as small Reynolds numbers, even if no inertial range is established [7]. Figure 2 displays, for the unmagnetized interstellar gas, (|AV| ) (top of left panel) and (|AV| ) (bottom of left panel) as functions of (|AV| ) and its best fits in dashed lines with slopes 0.73 and 1.57 corresponding to the scalings of £(2) and C(6), respectively. These scalings are different than those predicted by the K41 theory given by p/3 and similar to those proposed by Boldyrev [4]. More generally, the structure functions can be

log < | AV I"1 > P

Figure 2. Left: Log-log plot of <|AV|2) (top panel) and ( |AV|6) (bottom panel) as function of (|AV| ) and its best fits in dashed lines. Right: Comparison between theory (plus MHD simulations) and experiments of the exponents £(p) vs. order p.

written as Sp(l) oc 1^P\ where £(p) is given by C(p)/C(3) = 7P+C (1 - Sp) , with C = (1 — 37)/ (l — £3) and £(3) = 1; £ is a measure of the degree of intermittency of the flow, C (the Hausdorff codimension of the support of the most singular dissipative structures) is related to the structures' Haus­dorff dimension D by C = 3—D. In incompressible flows this corresponds to one-dimensional vortex filaments [3], hence C = 2, while the most singular dissipative structures in supersonic turbulence are two-dimensional shock fronts [4], and in fully developed MHD turbulence these are 2D micro­current sheets [5]; hence C = 1. 7 is related to very high order moments

22

and has the value of 1/9 for incompressible flows [3], with a similar value

quoted by [4,s] for supersonic HD and MHD turbulence. Hence, E 3 = 2 /3

or 1/3 if C = 1 or 2. The degree of intermittency in the compressible

turbulence is higher than in the incompressible case. In Kolmogorov tur­

bulence Q{p) = p/3, which implies tha t C = 0 independently of the value

of S . A comparison between the different theoretical scalings and the ones

derived from the MHD run is shown in Figure 2. Although the relative

scalings, which express the dependence of the moments a t different orders,

are universal, they show unambiguous departure from the Kolmogorov law

due to intermittency of interstellar turbulence. For further discussion on

these results see [6].

4. F inal R e m a r k s

In subsonic turbulence energy is injected at the outer scales and transferred

to the smallest scales, with dissipation by molecular viscosity setting in at

the Kolmogorov inner scale. Dissipation is a passive process as it proceeds

at a ra te determined by the inviscid inertial behaviour of the large eddies.

Such an energy cascading corresponds to a divergence-free behaviour of

the flow in the inertial range. However, the ISM is a compressible medium

swept up by shocks, which are in general more efficient in dissipating energy,

although most of it occurs again at small scales through low Mach number

shocks.

This research is supported by Portuguese Science Foundation (FCT)

through projects BSAB-455 to M.A. and P E S O / P / P R O / 4 0 1 4 9 / 2 0 0 0 to

the authors.

R e f e r e n c e s

1. M. A. de Avillez, Mon. Not. R. Astron. Soc. 315, 479 (2000); M. A. de Avillez and D. Breitschwerdt, Astron. & Astrophys. 425, 899 (2004); 436, 585 (2005).

2. A. N. Kolmogorov, C.R. Acad. Sci. URSS 30, 301 (1941). 3. Z.-S. She and E. Leveque, Phys. Rev. Lett. 72, 336 (1994). 4. S. Boldyrev, Astrophys. J. 569, 841 (2002). 5. H. Politano and A. Pouquet, Phys. Rev. E 52, 636 (1995). 6. M. A. de Avillez and D. Breitschwerdt, Phys. Rev. Lett., submitted (2005). 7. R. Benzi, S. Ciliberto, R. Tripiccione, C. Baudet, F. Massaioli, and S. Succi,

Phys. Rev. E 48, R29 (1993). 8. S. Boldyrev, A. Nordlund, and P. Padoan, Phys. Rev. Lett. 89, 31102 (2002).

ASTEROSEISMOLOGY A N D VARIABILITY OF Y O U N G STARS *

F. J. G. P I N H E I R O

Centro de Astrofisica da Universidade do Porto

Rua das Estrelas SN

4150-726 Porto, Portugal E-mail: fjgp@astro.up.pt

This article reports the analysis of the seismic properties expected for Pre-Main Sequence (PMS) stars. That study concluded that Christensen-Dalsgaard (CD) diagrams allow to constrain fundamental characteristics of low mass PMS objects (M < 1.5 M©)- Finally, this work presents a preliminary evaluation of the condi­tions required to detect solar-type oscillations in PMS stars.

1. Introduction

Asteroseismology is a valuable instrument to test stellar evolutionary mo­dels. In particular, Christensen-Dalsgaard (CD) diagrams1 can play an important role for constraining physical characteristics of solar-type stars5. Such diagrams are produced resorting to two typical properties of solar-type pulsations: the large (Av) and small (6v) frequency separations.

At the asymptotic regime8 p-mode pulsations display a typical frequency separation (Avn<i) between modes of the same degree (I) and consecutive overtone (n):

Avnj = vn,i - i/n-i,i oc Ai/ = - / — , (1)

where Av is half of the inverse core to surface sound travel time. Another frequency separation (Svnj) is found between frequencies vn<i and f„-i,i+2:

Av fRdcsdr OVn,l = Vn,l - Vn-\,l+2 OC — . (2)

Vfl,l JO G" T

•This work is supported by grant POCTI/CTE-AST/57610/2004 by FCT

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24

Equations 1 and 2 indicate that while Avn<i is sensitive to general stellar properties, Si/nii is sensitive to core structure changes (particularly to the sound speed gradient dcs/dr).

2. Christensen-Dalsgaard diagrams for PMS objects

Thirty PMS stellar models were used to analyse the pulsational properties of PMS objects. The different models represent 1 to 3 M 0 stars, with a solar metallicity, throughout six different evolutionary stages. In Figure 1 those stages are labelled from 1 to 6. The different stages range from the end of the Hayashi track (stage #1) to the ZAMS (stage #6) . The procedures and physical ingredients used to produce these models are the ones described at Ref. [3].

The pulsation frequencies expected for each model were computed using the code of linear adiabatic acoustic pulsations described at Ref. [4].

The large and small frequency separations used to compute the CD diagram were selected taking into account the highest amplitude oscillations expected for PMS stars. The maximum power pulsations were estimated using the predictions given at Ref. [2]. A normalised version of the small separation7 was used to compute the CD diagram that is displayed on the lower panel of Figure 1. That normalisation was done dividing 8u by Av.

As seen on the lower panel of Figure 1, different stellar models with more than 1.5 M© are located in the same region of the CD diagram. Consequently, such diagrams can only be used to study PMS objects with mass smaller than 1.5 MQ.

3. Solar-Type Oscillations in PMS Stars

Due to a lack of a definite model for the mechanism which drives solar-type oscillations, the amplitude and frequency of the maximum power solar-type pulsations are estimated by means of a scaling to the Sun2. In this manner, the amplitude of the maximum power for solar-type oscillations displayed by PMS stars should lie between 2 and 100 parts per million in magnitude. The period of these pulsations should range from 5 minutes to 1 hour.

4. Finding Oscillations in TTS

For the purpose of determining if asteroseismic techniques can be applied to analyse PMS objects, one has to find if the pulsations displayed by those objects can be detected.

25

2.0

1.5

^ 0.5 o

0.0

- 0 . 5

4.10 4.00 3.90 3.80 3.70 3.60 Log(Teff)

0.12

i 0.10 <a

0.08

0.06

50 100 150 Af (/j.Hz)

Figure 1. Position of PMS models with 1 (>), 1.5 (o), 2 ( A ) , 2.5 ( • ) and 3M Q ( v ) , in the HR diagram (top panel) and respective position in the CD diagram (bottom panel). The grey symbols correspond to models located near the end of the Hayashi track (stage # 1 ) , while the filled black symbols correspond to models at the ZAMS (stage # 6 ) . In the upper panel, the lines correspond to 1 - 3 M Q PMS evolutionary tracks. In the lower panel, the solid lines pass over the models with the same mass, while the dashed lines pass over the models with the "same stage label".

To achieve this goal, numerical simulations were carried out in order to find out the lowest pulsation amplitude that can be detected in a dataset with a given length. In the simulations it was attempted to identify a periodic signal, with a given amplitude and frequency, which had been previously added to a dataset representing observations from a T Tauri star (TTS). This method is described in more detail in Ref. [6].

Random noise can not reproduce the typical variability of TTS such as variable accretion. For this reason real observations of the Classical TTS (CTTS) DI Cep were used to generate the datasets. These observations were taken at the lm Jacobus Kapteyn Telescope (ING - La Palma) on November/December 2001. The data was obtained in four nights, in blocks

26

of 2.5 hours per night, with a sampling interval of 2.5 minutes. Several of

these blocks were randomly combined in order to simulate longer datasets .

The simulations involved the use of 90 days datasets (maximum duration

of Eddington's asteroseismic programs). The weakest signals detected on

these preliminary tests had amplitudes of a few tenths of a milimagnitude.

5. C on c lu s ion s &; Further D e v e l o p m e n t s

From the analysis of the CD diagram it was concluded tha t these diagrams

can be used to study PMS stars with less than 1.5 M©. Yet, the effect of

the stellar metallicity on PMS CD diagrams has to be evaluated.

According to the results presented in Sees. 3 and 4 it seems unlikely to

detect solar-type oscillations in DI Cep using a 90 days dataset . However

other C T T S have to be analysed before making a generalisation for these

objects.

A similar s tudy involving Weak T T S must be performed. For these

objects accretion rate variations do not play a role as important as in the

case of CTTS . Nevertheless in this case flaring events need to be taken into

account.

One should also recall tha t solar-type oscillations are multi-periodic.

Consequently, the case where several periodic signals are present in the

da ta must be considered.

Exoplanet search programs, like those available with the C O R O T mis­

sion, allow to obtain datasets with a sampled t ime longer than 3 months.

Therefore longer datasets should be considered.

R e f e r e n c e s

1. J. Christensen-Dalsgaard, Space Research in Stellar Activity and Variability, 11 (1984)

2. H. Kjeldsen and T. R. Bedding, A&A, 293, 87 (1995) 3. J. P. C. Marques and J. Fernandes and M. J. P. F. G. Monteiro, A&A,422,

239 (2004) 4. M. J. P. F. G. Monteiro, Seismology of the Solar Convection Zone, PhD Thesis,

Queen Mary and Westfield College (1996) 5. M. J. P. F. G. Monteiro and J. Cristensen-Dalsgaard and M. J. Thompson,

ESA SP-485: Stellar Structure and Habitable Planet Finding, 291 (2002) 6. F. J. G. Pinheiro and M. J. P. F. G. Monteiro and D. F. M. Folha, ESA

SP-538: Second Eddington Workshop: Stellar structure and habitable planet finding, 385 (2004)

7. I. W. Roxburgh and S. V. Vorontsov, A&A, 411, 215 (2003) 8. M. Tassoul, ApJS 43, 469 (1980).

ON THE PROBLEM OF MAGNETIC BRAKING*

J. M. FERREIRAj A. AIBEO*AND J. LIMA5

Centro de Astrofisica da Universidade do Porto, R. das Estrelas, Porto, Portugal

We examine the effect of the surface magnetic flux distribution on the coronal field topology. This preliminary study is motivated by the observational evidence for high magnetic flux concentration near the stellar poles of rapidly rotating young stars, and whether this has important consequences on the magnetic braking effi­ciency. We find that the coronal magnetic field rapidly expands to regions of low magnetic pressure creating a relatively smooth magnetic field with no memory of the surface radial field latitudinal distribution. Thus, our results indicate that this effect does not determine a reduction in the efficiency of magnetic braking.

1. Introduction

Magnetic braking by a wind is based on the principle that when gas emitted from a star is kept corotating with the star by magnetic torques, it will transport significantly more angular momentum outwards than gas that conserves its angular momentum [1].

The presence of rapidly rotating late-type stars in young clusters implies that there must be some limitation to the efficiency of magnetic braking during the pre-main sequence phase (e.g. [2]). One possibility is that beyond some rotation rate the magnetic field strength no longer increases with increasing rotation rate, i.e., the dynamo saturates [3]. But several alternatives to dynamo saturation have been suggested. Among others, the concentration of magnetic flux near the poles of rapidly rotating stars may lead to a saturation in the angular momentum loss rate [4, 5]. The idea that the concentration of magnetic flux near the poles can mimic dynamo saturation is based on basic principles: the Alfven radius is large near

-This work was partially supported by grant POCTI/CFE-AST/55691/2004 approved by FCT and POCTI, with funds from the european community program FEDER. tUniversidade dos Acores, Angra do Heroismo, Portugal, miguelf@mail.angra.uac.pt 'Escola Superior de Tecnologia de Viseu, Viseu, Portugal, aaibeo@infante.ipv.pt § Departamento de Matematica Aplicada, FCUP, Porto, Portugal, jlima@astro.up.pt

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28

the poles where the magnetic field is large, but small near the equator where the magnetic field is weak. As wind braking comes mainly from the contributions of low and intermediate latitudes, the overall effect is a reduction in the braking efficiency when compared with a homogeneous surface field distribution with the same total magnetic flux. It is implicit to this argument that the coronal radial field has a latitudinal distribution similar to the surface radial field.

2. The model

We consider an axisymmetric poloidal magnetic field in an atmosphere with negligible mass and pressure. To allow for the effect of the wind without di­rectly solving the complicate set of equations, we prescribe a certain amount of magnetic flux to be open. We make use of a family of analytical solutions to construct axisymmetric, totally or partially open, potential fields with equatorial current sheets outside a unit sphere [6]. The magnetic field can be expressed in spherical coordinates in terms of the stream function Z:

B = 1 (idZ dz) (i) r sin 0 \r o6 'fir 'J w

The stream function is given by a linear superposition of basic functions Zn, which are developed from the oblate spheroidal harmonics and classified according to the harmonic order n. We construct a magnetic field with its surface flux concentrated at the poles and compare it with a dipole-like field.

3. Results

3 .1 . Fully open magnetic fields

We first consider fully open fields in accordance with the picture presented in [4]. In Fig. 1 we represent the radial field strength as a function of co-latitude for different radial distances from the stellar centre for the two cases considered. The two radial fields latitudinal distributions are very distinct near the surface of the star, but rapidly become similar approaching the split monopolar field. For surface fields concentrated near the poles, the field lines that emerge at high latitudes are driven toward low latitudes (cf. Fig. 2).

29

i

0 . 8

0 . 6

u

0 . 4

0 . 2

0

0 0 . 2 5 0 . 5 0 . 7 5 1 1 .25 1.5 CO- l a t i t u d e

Figure 1. Fully open fields. The radial field latitudinal distribution: at the surface (full line), at r = 4R» (short dashed) and at r = 8R* (long dashed). The thick lines represent the poleward concentrated field and the thin lines the dipole-like field. For a clearer representation all the radial fields are set to unity at the pole.

4

2

0

- 2

- 4 0 2 4 6 8

Figure 2. Fully open fields. The lines of force of the dipole-like surface flux distribution (dashed line) and the polar concentration of flux (full line).

3.2. Partially open magnetic fields

The presence of closed loops, or dead zones, reduces the braking efficiency [7]. Here, we study field topologies with open and closed regions and find that the results obtained for fully open magnetic fields can be extended to more general field configurations. The results obtained are similar to the fully open magnetic configuration (see Fig. 3).

30

Figure 3. Partially open fields. The lines of force of the dipole-like surface flux distri­bution (dashed line) and the polar concentration of flux (full line). For the later case notice the field lines bending towards the equator. The field opens up at r=3R«.

4. Discussion and conclusions

We show that very different surface flux distributions give rise to similar coronal fields. For surface fields concentrated near the poles, the field lines that emerge at high latitudes are driven towards low latitudes. Physically, this is simply a consequence of the very large magnetic pressure difference between high and low latitudes. Therefore, a strong field near the pole and a weak field near the equator at the stellar surface do not imply a strong field near the pole and a weak field near the equator in the corona. Some of the physics neglected in this model could limit the expansion of the polar field to low latitudes. Namely, a high equatorial gas pressure and the magnetic pressure buildup near the equator due to rotation. This question is presently being addressed with an analytical wind model [8].

References

1. E. Schatzman Ann. Astrophys. 25, 18 (1962). 2. S. A. Barnes and S. Sofia, ApJ462, 746 (1996). 3. K. B. Macgregor and M. Brenner, ,4pJ376, 204 (1991). 4. S. K. Solanki, S. Motamen and R. Keppens, A&A 325, 1039 (1997). 5. D. L. Buzasi, ApJ 484, 855 (1997). 6. B. C. Low, ApJ 310, 953 (1986). 7. L. Mestel, MNRAS 138, 359 (1968). 8. A. Aibeo, J. M. Ferreira and J. Lima, in preparation.

A FIRST STEP FOR AUTOMATIC STELLAR PARAMETER DETERMINATION

S. G. SOUSA

Observatorio Astronomico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal

& Centro de Astrofisica da Universidade do Porto,

Rua das Estrelas, 4150-762 Porto, Portugal

The determination of stellar parameters is essential for the study of stellar astro­physics. Spectroscopy is one of the best ways to obtain fundamental parameters of a star. In this work we are testing and developing software to work with high resolution spectra (eg. HARPS) and obtain stellar parameters in an automatic, fast and effective way.

1. Introduction

To determine stellar parameters there are two major techniques that we can use: spectroscopy or photometry. Using photometry we can take a field of many stars and "quickly" obtain some of the individual stellar parameters. To get parameters using spectroscopy we are obliged to spent more time to analise individual spectra of a star. The other big difference is the accuracy of the results. For the parameters we are dealing with in this work we have a higher acuracy when using spectroscopy.

We determine parameters like the effective temperature, T e / / , the sur­face gravity, logg, and the metallicity, [M/H], using spectroscopy. The standard technique based on the iron ionization balance is used and the abundances are determined in Local Thermodynamical Equilibrium (LTE). See Santos et. al. 2000 for details. Using this method we need to measure equivalents widths of several iron lines in the stellar spectra. With this goal we are testing DAOSPEC, a new automatic code devel­oped by P. Stetson & E. Pancino (DAOSPEC, Stetson & Pancino 2005, http://cadcwww.hia.nrc.ca/stetson/daospec/). Among others tasks, this code measures equivalent widths in an automatic manner.

31

32

2. Testing DAOSPEC

2.1. Using the Solar spectrum

Our main purpose is to test equivalent width measurements. We will com­pare the calculations from DAOSPEC with the hard "hand made" mea­surements obtained using the IRAFa routine "splot" within the "echelle" package. We are also concerned about the reaction of DAOSPEC to dif­ferent types of spectra. Therefore we will test the reaction of this code for spectra with different rates of noise and instrumental resolutions.

The Sun is used as our object of study. For this purpose we used the Kurucz Solar Atlas and produced from it several spectra with different rates of artificial noise and resolution. The noise was created using a Gaus­sian distribution, and the instrumental resolution was introduced using the "rotin3.f routine in the SYNSPECb software of Hubeny & Lanz (1994). We measure equivalent widths of iron lines in two different regions of the visual spectrum of the sun because of the difference of the level of line pop­ulation. We choose 27 in the interval [4400A-4650A] and 36 in the interval [6000A-6300A]. Note that the first interval is more line populated than the second.

In Fig. 1 we show the comparison between the measurements made by DAOSPEC (y axis) and the "hand made measurements" (x axis). In the figure we can see the slope of the linear fit to the points (dashed line - as the slope gets near 1, better results we have), the number of lines identified by DAOSPEC, the RMS and mean difference of the results. The points are all very close to the identity line (filled line). We note a slightly better result for the less line populated region of the spectrum as expected.

In Fig. 2 we show how these values displayed on the box in Fig. 1 change when fixing resolution (expressed in Full Width Half Maximum, FWHM ~ O.IOA) and varying the noise. We see good results except for cases with a lot of noise (e.g. s/n ~ 10).

We have also tested stetting the noise to s/n ~ 100 and varying the resolution. The results show that the slope of the linear fit to the points was also very close to 1, and almost all lines are well identified until we reach resolutions of FWHM around 0.50A. Again we see best results in the less line populated region of the spectrum.

a IRAF is distributed by National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation, USA,

http://tlusty.gsfc.nasa.gov/index.html

33

s40QO-5000.JwO-10-sn0100 s6000~7000-fw0_1D_sn0100

' e l n r - • nQ471DM*

n° id lines : 25.000000 mean diference _ : 4.0085183

. . / / - • '

-

Figure 1. Comparasion between DAOSPEC and 'hand made' measurements in two different regions of the spectra for s/n ~ 100 and R ~ 50000. Filled line: identity line; Dashed line: linear fit; Left: [4400A-4650A]; Right: [6000A-6300A]

10 25 50 100 250 500 2000

«/" fwhm= O l 0 0 0 0 0

.1 10 25 50 » 250 500 2000

0.100000

1.1

1 I U

* 0.9

«s i 32 • 30

fwh

0 25

m -

50

0.100000

100 250 500 201

0.100000

100 250 500 2000 25 50 100 250 500 ;

fwhm- 0.100000

il

10 25 50 100 250 500 2000 «/" f whm- 0.100000

6 o 250 500 Z000

Figure 2. Variation of the rms, slope, n of lines and mean difference seen in Fig. 1 when fixing resolution (FWHM ~ 0.10 A) and varying the noise level.

2.2. Testing with real data

DAOSPEC seems to works well with different sets of resolutions and even with high noise levels. In this section we report the results of DAOSPEC in a big sample composed of 62 stars. The spectra was collected with the FEROS spectrograph (2.2m ESO/MPI telescope, La Silla, Chile, R = 50.000, s/n ~ 200 - 400), on October 2004. The lines used to do this test are standard Fe I and Fe II lines used to determine stellar parameters. A list of this lines can be found in Santos et al. (2004). One of the parame­ters of DAOSPEC is the wavelength interval for the calculation. Using the full individual spectrum interval yielded a large dispersion of the measure­ments. This comes from the fitting of the continuum level and, therefore, we considered small intervals, 500A wide, instead. The results for all stars were good. This can be seen in Fig. 3 where most of the points are close to the identity line (filled line). However, there seems to be a small under­estimate of the measurements made by DAOSPEC with a mean value of

34

about 3 mA. Using the slope obtained with our sample of 62 stars (more

than 3000 lines) we can easily correct this small offset.

All s tars in the plot (all spec)

0 50 100 150 IRAF EWs (mA)

Figure 3. DAOSPEC vs. 'hand made' measurements of equivalent widths for 3257 lines in a sample of 62 stars. Filled line: identity line; Dashed line: linear fit.

3 . C o n c l u s i o n s

DAOSPEC seems to be a good software for the measurement of equivalent

widths. It reacts fairly well to bad resolutions and relatively high noise

levels. However, we must be carefull on how to use it, as it works bet ter

using little portions of a whole spectrum at a time. There seems to be a

small underest imate of the DAOSPEC measurements by about 3mA (mean

value) tha t can be easily corrected.

A c k n o w l e d g m e n t s

Support from Fundagao para a Ciencia e a Tecnologia (Portugal) in the form

of a scholarship (reference SFRH/BD/17952/2004) and a grant (reference

POCI /CTE-AST/56453/2004) is gratefully acknowledged.

R e f e r e n c e s

1. Hubeny, I., Lanz, T., Jeffery, C.S., 1994, TLUSTY & SYNSPEC - A user's guide

2. Santos, N. C , Israelian, G., & Mayor, M. 2000, A&A, 363, 228 3. Santos, N. C , Israelian, G., & Mayor, M. 2004, A&A, 415, 1153 4. Stetson, P. B., & Pancino, E. 2006, in preparation

G I A N T T R A N S I T I N G P L A N E T S OBSERVATIONS - G I T P O

C. AFONSO

Max-Planck Insitut fur Astronomie, Konigstuhl 17,

69117 Heidelberg, Germany E-mail: afonso@mpia.de

The search for extrasolar planets is nowadays one of the most promising science drivers in Astronomy. The radial velocity technique proved to be successful in planet hunting, harvesting more than a hundred planets to date. In these last years, the transit method has come to fruition, with the detection of seven Jupiter-mass extrasolar transiting planets in close-in orbits (< 0.05 AU). Currently, the radius of planets can only be determined from transiting planets, representing the principal motivation and strength of this technique. The MPIA is presently building the Large Area Imager (LAIWO) for the lm telescope in the Wise Observatory, Israel. LAIWO will have a field of view of one square degree. An intensive search for extra-solar planets will be performed with the lm Wise telecope, together with the 1.2m MONET telescope in Texas. We will monitor three fields at a given time during three years and more than 200 nights per year. We expect several dozens of extra-solar planets.

1. Introduction

Extrasolar planet searches have gained major importance in the recent years and revealed itself as one of the most promising science drivers in Astron­omy. Unexpected results have led to new clues about the formation and evolution of planets. An example is the detection of massive planets, with Jupiter masses, at short periods P < 10 days, indicating that a migration process took place, after acquiring the bulk of their mass.

The radial velocity (RV) technique proved to be successful in planet hunting, harvesting more than a hundred planets to date1 2 , 1 1 . Recently, the Earth-mass range was attained with the detection of several Neptune-mass planets with masses equal to 7.5, 14, 18 and 21 M0

16>17>13-5. Although this technique is undoubtly successful, the degeneracy between the planetary mass and the inclination angle of the orbit, only allows to obtain a minimal mass for the planet.

Another promising method has come to fruition in the recent years,

35

36

with the detection of nine Jupiter-size transiting extrasolar planets in close-in orbits (< 0.05 AU) : HD209458b6, HD14902618 and HD189733b4, de­tected originally with radial velocity. Five planets found by the OGLE group: OGLE-TR-56b9, OGLE-TR-113b and OGLE-TR-132b2, OGLE-T R - l l l b 1 5 and OGLE-TR-10b3 '10, and TrES-11 , detected by the STARE telescope of the Trans-Atlantic Exoplanet Survey.

Planetary transits, in addition to the mass of the host star and the orbital radius, yield the radius of the planet,and the inclination angle, pro­vided the light curve has a high photometric accuracy, a high time sampling and the radius of the parent star is known or a stellar mass-radius relation is assumed. Currently, the radius of planets can only be determined from transiting planets, representing the principal motivation and strength of the transit technique. A radius measurement is an important quantity, since it allows to constrain the evolutionary and migration history of the planet and to infer its composition and atmosphere through evolutionary models. Furthermore, transit surveys do not pre-select the target stars to be monitored, as radial velocity searches do.

In the coming years, several hundred transiting planets are expected to be discovered from the ground, with more than 20 experiments on-going or being planned19, as well as from space with missions such as COROT 7 and Kepler8.

2. The M e t h o d - Planetary Transits

The detection method relies on the temporary drop in the brightness of the parent star harboring the planet. If the planetary system is in a favorable orientation relative to the line of sight (nearly perpendicular to the plane of the sky), then once per orbit the planet passes between its star and the observer, causing an occultation or transit that results in a dip in the light curve (see figure 1). Since the fractional change in brightness SF (or transit depth) is proportional to the stellar surface eclipsed by the planetary disk, the planet's size Rp can be inferred from photometric measurements, provided the stellar radius is known (6F = ( jj^)2). For Jupiter-sized planets transiting sun-sized stars, the expected transit depth will be about 1%. If three or more transits can be measured and confirmed to be due to the same planet, the period P can be determined and hence from Kepler's third law P = ^/47r2a3/GM*, the orbital radius or semi-major axis a can also be inferred. Once the radius of the planet and the period are known, the inclination can be determined from the shape of the transit light curve, as

37

parameterized by the ratio of the duration of the transit's flat bottom to the total transit duration tr,

[ l -R p /R*] 2 - [ (D/R*)cosi] 2

[1 + Rp/R*]2 - [(D/R*) cos i]2

The total transit duration being equal to

/tflat \2

tx (1)

tT^\/(1+|)2-(cC0Si)2 (2)

3. The Project - Giant Transiting Planets Observations -GITPO

The Max-Planck fiir Astronomie, the University of Tel Aviv and the Stern-warte of Gottingen initiated a transit search program, the Giant Tran­siting Planets Observations - GITPO, funded by the Max-Planck fiir As­tronomie and the German-Israeli Foundation (GIF). The aim of the project

19.fi

•Ifi.i

OGLE-TR-3B P=1.21190 {Says)

fc£_J i_J L.

*m *~ y~r-: i j " p r vi r"T~T"T~Ti

- k HUM

...i...I..J„.J„.5....i....A..4-...i...A...i..J..-.

L'l _1 I i I J I i i _ t

Figure 1. Light curve of OGLE-TR-56, the first planetary system discovered by the transit method. The extra-solar planet has a mass of 0.9 M j u p and a distance of 0.023 AU to its parent star (Udalski et al. 2002).

38

is to detect Jupiter-size extra-solar planets around main-sequence stars with magnitudes down to V=17. Currently, a Large Area Imager for the Wise Observatory (LAIWO) is beeing built at the Max-Planck fur Astronomie. LAIWO is composed by an array of four front-side illuminated Lockheed CCDs with 4Kx4K pixels, with a pixel size of 15/rni. The camera will be mounted on the 1 m telescope in the Wise Observatory, in the Negev desert, Israel. The field of view will be one square degree. The observing strat­egy will consist in the continuous monitoring of three fields at any given time, until 3,000 images are acquired. We anticipate to have more than 200 nights allocated per year during three years, covering a total sky surface of 30 deg2. Observations will be coordinated with the 1.2m MONET (see reference) telescope located in Texas, USA, operated by the University of Gottingen, Germany. The network of these two telescopes will increase the number of measurements, enhancing the expected number of planets. Dozens of transiting extra-solar planets are expected to be found over the three year observation campaign.

References

1. Alonso, R. et al. , ApJ 613L, 153 (2004) 2. Bouchy, F. et al. , A&A 421, L13 (2004) 3. Bouchy, F. et al. , A&A 431, 1105(2005) 4. Bouchy, F. et al. , A&A 446L, 15B (2005) 5. Butler, B. et al. , ApJ 617, 580B (2004) 6. Charbonneau, D. et al., ApJ 529L, 45 (2000) 7. COROT , http://sci.esa.int/home/corot/index.cfm 8. Kepler, http://www.kepler.arc.nasa.gov 9. Konacki, M. et al., Nature 421, 507 (2003) 10. Konacki, M. et al., ApJ 624, 372 (2005) 11. Marcy, G.& Butler, R .P., ApJ 464, L147 (1996) 12. Mayor, M.& Queloz, D. , Nature 378, 355 (1995) 13. McArthur, B. et al. , ApJ 614L, 81M (2004) 14. MONET,

http://monet.uni-goettingen.de/cgi-bin/WebObjects/MonetPortal 15. Pont, F. et al. , A&A 426, L15 (2004) 16. Rivera, E. et al. , ApJ 634, 625 (2004) 17. Santos, N. et al. , A&A 426L, 19S (2004) 18. Sato, B. et al. , ApJ 633, 465S (2005) 19. Planets Encyclopedia , http://www.obspm.fr/planetes 20. Udalski, A. et al. , Acta. Astron. 52, 115 (2002)

P R O B I N G T H E S T R U C T U R E A N D A T M O S P H E R E S O F E X T R A - S O L A R P L A N E T S

N. C. SANTOS

Centro de Astronomia e Astrofisica da Universidade de Lisboa, Observatorio Astronomico de Lisboa,

Tapada da Ajuda, 1349-018 Lisboa, Portugal

E-mail: nuno.santos@oal.ul.pt

In this paper we review the recent results concerning the detection of extra-solar planets, with particular emphasis on the cases where a transit event is measured.

1. I n t r o d u c t i o n

From 1995 to the present, following the discovery of the first extra-solar

planet orbiting a solar type s tar 1 6 , about 160 giant planets have been an­

nounced, showing tha t these are common around stars in the solar neigh­

borhood3 ' . The first rocky worlds may have been found2 4 '1 8 , 2 8 , opening the

way to the discovery of earth-like planets.

P lanet search programs have unveiled the presence of giant planets with

a huge variety of orbital characteristics, very different from the Solar System

giants. These findings are thus defying the models of planetary formation

and evolution25 . Fortunately, the statistical analysis of the newfound plan­

ets, as well as of their host stars, are now opening the possibility to revise

the theories of planetary formation and evolution2 2 , 2 3 '2 8 '9 '1 2 .

So far, most of the known extra-solar planets have been unveiled by

the use of the Doppler radial-velocity technique. Alone, this only gives us

information about the orbital parameters of the planets and their mini­

m u m masses. No direct information is given about the planetary physical

properties. A complementary technique tha t can give us direct physical

information about the planet itself is the photometric t ransi t technique.

Until recently, however, only in a few cases was it possible to measure the

aFor a continuously updated version see table at http://obswww.unige.ch/exoplanets

39

40

s'"'P = °-4

-

! -

/ T

/ / 1 "

{V" i y^ 1 r * • 1

M , - ' M ~H ^ , M

r ^ ~

"""1

r

^--''

L t J- • —1 , ' ' D

- / D ,''p = 1.0

• ' ' / *

i _ l i i i I i i i I i i i L_ 0.4 0.8 1.2 1.6

M a s s ( M J„ P )

Figure 1. Mass-radius diagram for the giant planet companions for which a transit event has been detected. The position of Jupiter and Saturn, the two giant gaseous planets in the Solar System, is also marked (open squares). Two iso-density curves, with densities of 0.4 and 1 .0gem - 3 are shown for comparison.

light dimming of the star as its planet crossed the stellar disk. The realm of data coming from these discoveries is opening, for the first time, the possibility of probing the planetary atmospheres and internal structure.

2. Transiting planets

One particular outcome of the extra-solar planet discoveries was the de­velopment of several photometric surveys to search for planetary transits. The most successful of these added hundreds of new candidates to the lists27'1. Unfortunately, due to the degenerate state of the matter in very low mass stars, there is a strong degeneracy between the radius of objects with masses between the mass of Jupiter and about 10% the mass of the Sun (~100 Jupiter masses)2'20. Given that the transit method will only give information about the radius of the transiting body, it is thus not possible to determine its mass from simple photometric measurements.

The solution to this problem implies the use of spectroscopy, but most of all, of radial-velocity measurements. These will give important informa­tion about the stellar properties (stellar mass and radius), and provide the minimum mass of the orbiting planet3. Using these complementary tech-

41

niques we can then accurately know the mass, radius, and mean density of a transiting planet.

From the hundreds of transiting candidates found by photometric surveys, subsequent radial-velocity follow-up studies have shown that most were either low mass stars, grazing stellar binaries and blends, or false candidates3'20'21. However, a few of the candidates were indeed planets14 '3 '19 '1 '15. Together with a few other transit cases among the plan­ets discovered with radial-velocity techniques5'13'26'4, these discoveries gave the possibility, for the first time, to populate the mass-radius diagram in the Jupiter mass range (see figure), and to confront the observations with internal structure models11.

The new detections have also raised a lot of scientific problems. Part of the discovered transiting planets14 '3 have orbital periods of the order of 1-2 earth days. This is in clear contrast with the known lower limit close to 3-days observed for (hot-jupiter) giant planets discovered by the radial-velocity technique25. Whether this is simply the result of a detec­tion bias, or if this can be explained by some physical process, is now a matter of debate10. Furthermore, among the confirmed transiting planets, HD2094585 '13 has the lowest and most anomalous mean density11. Curi­ously also, a relation between the planet mass and the orbital period also seems to exist17. The understanding of these issues may give us some im­portant clues about the processes of giant planet formation and evolution.

In addition to the internal structure, the detection of transiting planets opens a new possibility to study the planetary atmospheres. When the planet crosses the stellar disk, its upper atmosphere acts as a filter, absorb­ing the light coming from the star at some preferential wavelengths that correspond to atomic/molecular transitions occurring in its atmosphere. Due to this effect, sodium absorption features were detected in the at­mosphere of the planet orbiting HD2094586. Further observations have also recently suggested that this giant planet is evaporating, as carbon and oxygen atoms are blown away along with its hydrodynamically escaping hy­drogen atmosphere30'31. Finally, recent IR measurements with the orbiting Spitzer Infra-Red telescope have measured the IR flux from the planet8'7, using the anti-transit moment to observe the decrease in the IR-flux as the planet passes behind the stellar disk. These measurements gave the first direct estimates of the planetary temperatures.

42

A c k n o w l e d g m e n t s

Support from Fundacao para a Ciencia e a Tecnologia (Portugal) to N.C.S.

in the form of a scholarship (reference SFRH/BPD/8116 /2002) and a grant

(reference POCI /CTE-AST/56453/2004) is gratefully acknowledged.

R e f e r e n c e s

1. Alonso, R., Brown, T. M., Torres, G., et al., ApJ 613, L153 (2004) 2. Baraffe, I., Chabrier, G., Barman, T. S., et al., A&A 402, 701 (2005) 3. Bouchy, F., Pont, F., Santos, N. C., et al., A&A 421, L13 (2004) 4. Bouchy, F., Udry, S., Mayor, M., A&A, in press (2005) 5. Charbonneau, D., Brown, T., Latham, D., and Mayor, M., ApJ 529, L45

(2000) 6. Charbonneau, D., Brown, T. M., Noyes, R. W., and Gilliland, R. L., ApJ 568,

377 (2002) 7. Charbonneau, D., Allen, L. E., and Megeath, S. T., et al., ApJ 626, 523

(2005) 8. Deming, D., Seager, S., Richardson, L. J., and Harrington, J., Nature 434,

740 (2005) 9. Eggenberger, A., Udry, S„ and Mayor, M., A&A 417, 353 (2004) 10. Gaudi, B. S., Seager, S., and Mallen-Ornelas, G., ApJ 623, 472 (2005) 11. Guillot, T., Annual Review of Earth and Planetary Sciences 33, 493 (2005) 12. Halbwachs, J., Mayor, M., and Udry, S., A&A 431, 1129 (2005) 13. Henry, G. W., Marcy, G. W., Butler, R. P., and Vogt, S. S., ApJ 529, L41

(2000) 14. Konacki, M., Torres, G., Jha, S., and Sasselov, D., Nature, 421, 507 (2003) 15. Konacki, M., Torres, G., Sasselov, D. D., and Jha, S., ApJ, 624, 372 (2005) 16. Mayor, M. & Queloz, D., Nature 378, 355 (1995) 17. Mazeh, T., Zucker, S., and Pont, F., MNRAS 356, 955 (2004) 18. McArthur, B., Endl, M., Cochran, W.D., ApJ 614, L81 (2004) 19. Pont, F., Bouchy, F., Queloz, D., et al., A&A 426, L15 (2004) 20. Pont, F., Melo, C.H.F., Bouchy, F., et al., A&A 433, L21 (2005) 21. Pont, F., Bouchy, F., Melo, C.H.F., et al., A&A 438, 1123 (2005) 22. Santos, N. C , Israelian, G., and Mayor, M., A&A 373, 1019 (2001) 23. Santos, N. C , Israelian, G., and Mayor, M., A&A 415, 1153 (2004) 24. Santos, N. C , Bouchy, F., and Mayor, M., et al., A&A 426, L19 (2004) 25. Santos, N. C , Mayor, M., and Benz, W., Science 310, 251 (2005) 26. Sato, B., Fischer, D. A., Henry, G. W., et al., ApJ, in press (2005) 27. Udalski, A., Paczynski, B., Zebrun, K., et al., Acta Astronomica, 52, 1 (2002) 28. Udry, S., Mayor, M., and Santos, N.C., A&A 407, 369 (2004) 29. Udry, S., Mayor, M., Benz, W., A&A, in press (2005) 30. Vidal-Madjar, A., Lecavelier des Etangs, A., Desert, J.-M., et al., Nature

422, 143 (2003) 31. Vidal-Madjar, A., Desert, J.-M., Lecavelier des Etangs, A., et al., ApJ 604,

L69 (2004)

W H A T ' S G O I N G O N I N C A N I S M A J O R ?

A. M O I T I N H O

CAAUL, Observatorio Astronomico de Lisboa,

Tapada da Ajuda, 1349-018 Lisboa, Portugal

E-mail: andre@oal.ul.pt

G. C A R R A R O

Departamento de Astronomia, Universidad de Chile, Chile

and Astronomy Department, Yale University, USA

R. A. V A Z Q U E Z , G. B A U M E A N D E. E. G I O R G I

Facultad de Ciencias Astronomicas y Geofisicas de la UNLP, IALP-CONICET, Paseo del Bosque s/n 1900, La Plata, Argentina

We report the detection of a young stellar population (< 100 Myrs) in the back­ground of nine open clusters in the Third Galactic Quadrant. We find that the young background population in six cluster fields follows remarkably well the ex­pected pattern of the Norma-Cygnus spiral arm as defined by CO clouds. This population is exactly the same (the Blue Plume) recently detected in the direction of 3 intermediate-age open clusters in the same region, and suggested to be a 1-2 Gyr old population belonging to the Canis Major over-density1 '2. Both, distances and ages we find are incompatible with this scenario.

1. Introduction

The recent detection of the Canis Major (CMa) over-density3 (1 = 240°, b = -8°) produced a renaissance of interest in the third Galactic quadrant (3GQ). But if this over-density is widely believed to be the core of a galaxy being cannibalised by the Milky Way, the lively debate1,4 on its nature demands a clear picture of the structure of this poorly known region of our Galaxy. Unfortunately, the 3GQ has been largely ignored in the past and besides the presence of the Galactic warp, little is known about its structure. In particular, spiral structure has not been clearly mapped5.

For several years we have been conducting a systematic UBVRI photo­metric survey of open clusters in this part of the Galaxy6-9 to study the

43

44

structure of the Disc. In particular, young open clusters are privileged spiral tracers since their distances can be better determined than those of indi­vidual stars and their youth keeps them close to the spiral arms where they were born. In this contribution we report the detection of a distant young stellar population and discuss how this result casts considerable doubt on the interpretation of the CMa over-density as the core of an external galaxy.

2. Resul t s

v- . x

B5-

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1 T - • i i | i i

i.v'-.-.'

:.\

1 1 1 .

. •

, \

n i

p

• v \ V • \ .B6

1 A ° — ^ j f i £ ^ -•'S>V\.-.:

1 1 1 ..1 1 1 . J - . l . 1 l _ l _ J . I ^ _

•

•

; • •

:

V"-\'

0.5 1.5 1.5

B-V

Figure 1. CMD and TCD for NGC 2302. Lines are the empirical ZAMS fitted to the cluster sequence (dashed) and BP (solid). See text for details.

Analysis is exemplified in Fig. 1 which shows the Two Colour Dia­gram (TCD) and Colour-Magnitude Diagram (CMD) of the open cluster NGC 2302. Basic parameters (reddening, distance and age) were derived via Zero Age Main Sequence (ZAMS) and isochrone fits to the cluster se­quences in different photometric diagrams. Three distinct populations are seen in the CMD: The (1) cluster population revealed by the upper, bluer main sequences (MS). The MS is fitted with the ZAMS10 shifted to account for the effects of reddening and distance (dashed lines). A (2) fainter and more reddened young population indicated by filled squares. We are going to refer to this population as the Blue Plume (BP). The ZAMS fits to the BP are indicated with solid lines. The (3) Galactic disk field population.

The BP is also visible in the photometric diagrams of 8 other clusters. Analysis of our whole sample is underway and we expect more detections to come. The fits to the BPs provide us the parameters for this population in different Galactic directions. We notice that spectral types of the BP stars

45

go from B3-B5 to late A and F, showing that this population is actually younger than 100 Myr.

In Fig. 2, we plot the studied clusters and their BPs on the plane of the Milky Way. To help interpretation, we also plot the distribution of CO clouds (kindly provided by J. May and L. Bronfman ahead of publi­cation). Many of these clouds harbour IRAS sources, suggesting on going star formation.

Gal. Rotation

12.0

10.0

8.0

6.0

4.0

2.0

0.0

. ' 1

. 6

", i

i i i | i i

„ ° ° * ' Oo<?

, , , ! , ,

, 1 , , , 1 , , , 1

o 0

• °°-

*

I 1 1 , 1

. ,

°B

1 = I 1 .

-:

--

-

:

i i

- 1 2 . 0 - 1 0 . 0 -8 .0 -6 .0 -4 .0 -2 .0 0.0 ' X[kpc]

Figure 2. Sketch of the third quadrant of the Galactic plane. Open squares: clusters from our sample. Filled triangles: BPs. Open circles: CO clouds. Starred symbols: BPs from other studies, taken as evidence for the CMa galaxy. Large filled square: position of the CMa over-density. Filled circles: Open and globular clusters suggested to be possibly associated to CMa. Sun is at (0,0). Directions of Galactic Centre and rotation are indicated by arrows. Dotted circles mark two constant heliocentric distances (5 and 10 kpc).

The BP population of 6 cluster fields follows remarkably well the pattern defined by CO clouds. This pattern defines a stripe of young objects (stars and CO clouds) at the expected position of the Norma-Cygnus spiral arm of the Milky Way. It seems therefore that the existence of the Norma-Cygnus arm (often referred to as the Outer arm) in the Third Galactic Quadrant, previously not very clear, is a reality. Moreover, the arm extension is mostly detected low in the Galactic plane at +0.5 < b < —6.50, which is a clear effect of the Galactic warp. We also notice that three BPs do not follow the Outer arm, but they are much closer to the Sun and lie above the Galactic

46

plane. Interestingly, identical BPs in the fields of 3 other negative latitude open

clusters have been taken as evidence for the existence of a galaxy in CMa1,2. In particular, they have been interpreted as the last burst of star formation in that galaxy. However, those conclusions were not based on U band data which allows to unambiguously show that the BP contains young spectral types and is thus young.

Our findings support the idea that the BP in the CMa direction is a young population mostly associated to the Norma-Cygnus arm: It is young and it defines the same stripe pattern as CO clouds encompassing a significant sector (more than 40° in longitude) of the Third Quadrant, where the Outer arm is expected to lie.

Acknowledgements

A.M. acknowledges FCT (Portugal, grant SFRH/BPD/19105/2004). G.C. is supported by Fundacidn Andes. Programme SECYT-MAE: IT/PA03 -UIII/077 (Argentina) is acknowledged. This study used the Simbad and WEBDA databases.

References

1. Bellazzini, M., Ibata, R., Monaco, L., Martin, N., Irwin, M. J., & Lewis, G. F., 2004, MNRAS, 354, 1263

2. Martinez-Delgado, D., Butler, D. J., Rix, H.-W., Franco, Y. I., Pefiarrubia, J., Alfaro, E..J., & Dinescu, D. I., 2005, ApJ, 633, 205

3. Martin, N. F., Ibata, R. A., Bellazzini, M., Irwin, M. J., Lewis, G. F., & Dehnen, W., 2004, MNRAS, 348, 12

4. Momany, Y., Zaggia, S. R., Bonifacio, P., Piotto, G., De Angeli, F., Bedin, L. R., & Carraro, G., 2004, A&A, 421, L29

5. Russeil, D., 2003, A&A, 397, 133 6. Moitinho, A., 2001, A&A, 370, 436 7. Moitinho, A., Alves, J., Huelamo, N., & Lada, C. J., 2001, ApJL, 563,

73 8. Baume, G., Moitinho, A., Giorgi, E. E., Carraro, G., & Vazquez, R. A.,

2004, A&A, 417, 961 9. Moitinho, A., Carraro, G., Baume, G., & Vazquez, R. A., 2006, A&A,

445, 493 10. Schmidt-Kaler, T., 1982, Landolt-Bornstein, Group VI, Vol. 2b, Stars

and Star Clusters, p. 15 (Berlin: Springer)

STUDY OF THREE GALAXY CLUSTERS AT INTERMEDIATE REDSHIFTS

C. LOBO

Depto. de Matemdtica Aplicada e Centro de Astrofisica, Universidade do Porto Rua das Estrelas, 4.150 - 762 Porto, Portugal

E-mail: lobo@astro.up.pt

M. SEROTE ROOS*

Centro de Astronomia e Astrofisica da Universidade de Lisboa Tapada da Ajuda, 1349 - 018 Lisboa, Portugal

E-mail: serote@oal.ul.pt

We analyze the galaxy properties of 3 intermediate-z clusters, CL0048-2942, CL2245-3954 and CL2249-3958, searching for environmental effects. Member galaxies of the first 2 display very similar cluster-centric radial gradients in stellar populations and spectral classes; this is interpreted in terms of galaxy infall into the cluster, followed by truncation of star formation and passive evolution in lu­minosity. CL2249-3958 is a particular case, since it is a poorer system apparently made up of 2 sub-clumps infalling into one another along the line of sight.

1. I n t r o d u c t i o n

Environment strongly affects the properties of galaxies, eg. cluster and field

galaxies reveal different stellar populations. This can be due to the different

morphological mix3 . Whether this mix is driven by environment or set by

the initial density conditions of the region where the galaxies are born is

another issue. Looking at morphology and star formation history can help

to shed light on this question. This paper presents preliminary results on

the s tudy of galaxy spectral classes for 3 clusters at intermediate-z, with

the aim of contributing to this fascinating topic.

2. O b s e r v a t i o n s and d a t a r e d u c t i o n

The clusters were identified in the I-band EIS 5 by a matched filter-like

detection algorithm4 . BVRI photometry (ESO 3.6-m telescope) was then

*Work supported by grant ref. BPD/5684/01 of the FCT/Portugal

47

48

conducted to help selecting targets for follow-up spectroscopy, obtain infor­mation on cluster members, and make color studies. Spectroscopy (MOS, VLT) was carried out with R = 500 in [4450-8650] A. The data were re­duced according to standard procedures using IRAF. We obtained 73 galaxy spectra for CL0048-2942 and 68 spectra for both CL2245-3954 and CL2249-3958. Redshifts were measured according to the Tonry & Davis technique11. For CL0048-2942, 54 reliable redshifts were produced, from which 23 were identified as belonging to the cluster, at z ~ 0.64. For CL2245-3954, 47 redshifts were measured, of which 15 are from cluster members, at z ~ 0.65. For CL2249-3958, only 10 cluster members were found, at z ~ 0.56, from a total of 54 measured redshifts.

3. Stellar population synthesis

We have used a population synthesis analysis to determine the stellar con­tent (or evolutionary stage) of cluster galaxies at different radial distances from the cluster centre. Field galaxies, observed and analyzed in the same way, provide the term of comparison to deduce the impact of cluster envi­ronmental effects on the evolution of their member galaxies. To compute the stellar content, we performed a stellar population synthesis by means of a mathematical algorithm that gives a unique solution6. This method makes use of the equivalent widths (EWs) of all absorption features found in the spectrum. It considers a galaxy as being made up of a set of stars of different spectral types, luminosity classes and metallicities. This compo­sition will carry its own signature in the EWs of the absorption features. The method defines the galaxy composition by reproducing its signature as closely as possible, taking into account all EWs in the galaxy spectrum. This is done by matching the observed EWs of the galaxy with the stellar EWs of a combination of stars (by the least squares method).

The stellar database used in this work was compiled from the Pickles stellar library7 which gathers 131 stellar spectra of every spectral type and luminosity class from 1150 to 10620 A and R = 500, including some metal-rich and metal-poor stars. A total of 44 stars were chosen from this stellar library in order to cover the temperature/gravity parameter space as much as possible without being degenerate. 63 stellar features were then identified and the EW measured, for each star of the database.

The synthesis was performed for 44 galaxies in the CL0048-2942 field of view (19 belonging to the cluster), 45 galaxies in the CL2245-3954 area (13 belonging to the cluster) and 51 galaxies in the direction of CL2249-

49

3958 (10 being cluster members). The interpretation of the synthesis is made in terms of age, as well as luminosity class, of the stars that compose the most statistically significant solution for each galaxy. We have defined 3 age intervals: young (106 - 108 years), intermediate (around 109 years) and old (> 1010 years) stars; and 3 luminosity classes: dwarfs, giants and supergiants. Thus 6 different groups characterize the stellar populations of our galaxies: young main sequence, intermediate main sequence, old main sequence, young giants, intermediate giants and finally supergiants (which are naturally all young).

For CL0048-2942 (see Serote Roos et al. 2005 for further details on this system), we find population gradients within the cluster for 2 of the main population components, i.e., galaxies in the cluster core host older stars whereas the stellar populations of galaxies inhabiting the outer cluster regions are dominated by young, less evolved stars (i.e. supergiants). We then conclude that star formation is predominantly taking place in the outskirts of the cluster. And, in a general way, field galaxies in this line of sight reveal less evolved stellar populations.

For CL2245-3954 we also find population gradients within the cluster, but now for 4 of the main population components, i.e. old and intermediate age stars are more abundant in the centre of the cluster than in the out­skirts, whereas young stars dominate the stellar population as we approach the periphery of the cluster. Regarding field galaxies in this area, we find less evolved stellar populations than the ones obtained for members in the cluster centre. However, the periphery of the cluster does show younger populations than the ones found in the field.

Concerning CL2249-3958, no regions within the cluster could be defined due to the small number of cluster members (only 10), so no gradients were searched for. However, comparing the stellar populations found for the cluster, as a whole, with those of the field galaxies in the same line of sight, we find that the latter are, in general, less evolved.

These results point to the fact that a significant fraction of galaxies in clusters seems to have suffered a dramatic decrease of their star formation rate over the last ~ 1 - 1.5 Gyr, which could have been preceded by an intense burst of star formation (as seems to be the case of CL2245-3954). This stage is followed by a period of passive evolution in luminosity. These trends were also found elsewhere2'12'9 in other clusters at low and interme­diate redshifts, but by means of other methods. While mechanisms such as ram-pressure stripping, galaxy interactions and shocks with the intra-cluster medium could be invoked to explain these findings, more detailed

50

observations (such as galaxy morphologies, IR photometry and color gra­

dients within the galaxies) are needed in order to draw a clear scenario.

4 . Spec tra l c lasses

Following previous work1 '8 '1 2 , we have estimated the percentage of emission

line galaxies (EL), and post-star forming galaxies (K+A) in the clusters

and in the field. ELs are defined as having EW([OII]) > 10 A, whereas

K + A galaxies display EW([OII])< 5 A and EW(HS) > 5 A or (EW(HS) +

EW(Hy))/2 > 4 A or (EW(Hs) + EW{H^) + EW(Hp))/3 > 4 A. All other

galaxies are classified as normal (N). The following table summarizes our

results.

Table 1. Spectral classes, in percentages, for the 3 clusters and for all field galaxies in the the 3 lines of sight taken altogether (named superfield).

Sample

CL0048-2942 CL2245-3954 CL2249-3958

superfield

EL

35% 20% 40% 61%

K+A

13% 27% 0% 5%

N

52% 53% 60% 34% [0

< z >

0.64 0.65 0.56

.05,0.85]

Though statistics are poor with such small numbers, and prevent us

from drawing any firm conclusions, some trends do come up: as expected,

EL galaxies dominate the field sample, as opposed to N galaxies in clusters;

K + A s are more abundant in intermediate-z clusters relatively to the field

likely due to environment, if we don ' t consider the case of CL2249-3958

which, as already stated, is a particular system with atypical characteristics.

R e f e r e n c e s

1. Balogh, M. L., Morris., S. L., Yee, H. K. C , et al., ApJ 527, 54 (1999). 2. Balogh, M. L., Bower, R. G., Smail, I., et al., MNRAS 337, 256 (2002). 3. Dressier, A., ApJ 236, 351 (1980). 4. Lobo, C , Iovino, A., Lazzati D., and Chincarini, G., A&A 360, 896 (2000). 5. Nonino, M., Bertin, E., da Costa, L. et al., A&AS 137, 51 (1999). 6. Pelat, D., MNRAS 284, 365 (1997). 7. Pickles, A. J., PASP 110, 863 (1998). 8. Poggianti, B. M., Smail, I., Dressier, A., et a l , ApJ 518, 576 (1999). 9. Quintero, A. D., Hogg, D. W., Blanton, M. R., et al., ApJ 602, 190 (2004). 10. Serote Roos, M., Lobo, C., Durret, F., et al.,A&A 429, 101 (2005). 11. Tonry, J., and Davis, M., A J 84, 1511 (1979). 12. I ran , K.-V.H., Franx, M., Illingworth, G., et al.,ApJ 599, 865 (2003).

MODELLING THE WARM ABSORBER IN N G C 3783 WITH THE TITAN CODE

A. C. GONQALVES

CAAUL, Observatorio Astronomico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal

E-mail: adarbon@oal.ul.pt, anabela.darbon@obspm.fr

A. ROZANSKA

Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland

S. COLLIN, A.M. DUMONT, M. MOUCHET,

L. CHEVALLIER, R. W. GOOSMANN

LUTH, Observatoire de Paris-Meudon, 5 Place Jules Janssen, 92195 Meudon Cedex, France

The "Warm Absorber" (WA) observed in Active Galactic Nuclei (AGN) displays zones of different density, temperature and ionization. Our approach to the study of the WA relies on the assumption of total pressure equilibrium, which results in the natural stratification of the medium and allows to explain the presence of lines from different ionization states in many AGN observed by XMM-Newton and Chandra. We have used the photoionization code TITAN, developed by our team, to calculate a grid of constant total pressure models dedicated to fit the WA in NGC 3783. Our study shows that the WA can be modelled in pressure equilibrium. Finally, this work provides a good example of the application of the TITAN code to the study of the WA in AGN, and opens perspectives for its use by a larger community, through a grid of constant total pressure models to be made available via XSPEC and/or via Virtual Observatory facilities.

1. Introduction to the Warm Absorber

Many AGN exhibit X-ray absorption features caused by the presence of

highly ionized gas located on the line-of-sight of the central continuum.

Such a material is called "Warm Absorber" (WA) and is consistent with

gas photoionized by the hard X-rays produced near the central engine.

Early ASCA observations revealed the presence of ionized soft X-ray

absorption in ~ 50% of type 1 Seyferts; evidence for a WA was also found

in Seyfert 2s, Narrow Line Seyfert Is, BAL QSOs and even some BL Lacs.

With the advent of space X-ray observatories such as XMM-Newton and

Chandra, an important set of high quality data became available, providing

valuable information on the WA.

51

52

Spectra of type 1 AGN revealed the presence of tens of absorption lines, covering a wide range of ionization states, and blueshifted by hundreds to thousands k m s - 1 (an indication that the absorbing material is outflowing); in type 2 AGN, the data have shown the presence of emission lines.

Despite the undeniable improvements in our knowledge of the WA, some important issues remain a subject of debate, namely: (i) the location and geometry of the WA, (ii) the physical conditions of the absorbing/emitting gas, and (Hi) the implications of the WA in the energetics of the AGN. Trying to solve these questions requires not only high quality observations, as the ones provided by XMM-Newton and Chandra, but also an adequate treatement of the X-ray data through the use of reliable photoionization codes, calculating the full radiative transfer. We have addressed the above mentioned points through the study of the Warm Absorber in NGC 3783, for which unrivaled quality Chandra archive data are available; we have modelled the data using our photoionization code TITAN1'2, which sup­ports the assumption of pressure equilibrium and allows for a multi-angle analysis of the emergent spectra.

2. The Warm Absorber in N G C 3783

NGC 3783 is a bright (V ~ 13.5), nearby (z = 0.0097) Seyfert 1.5 galaxy observed in the Optical, UV and X-rays. The WA in this object has been discussed by several authors3 '4,5,6 based on Chandra and XMM-Newton spectra. Although the WA in NGC 3783 has been the object of many studies, these have assumed constant density or a dynamical state7 for the modelling. In addition, they all require multiple zones of different density, temperature and ionization; these are invoked to explain the large span in ionization observed in WA spectra.

Furthermore, when plotted on the S-curve of thermal equilibrium (log(T) vs. log(£/T), where T is the temperature of the medium in K and £ is the ionization parameter, in erg cms - 1 ) , these clouds lie on a vertical line of same gazeous pressure.

3. Data reduction and modelling

We have searched the Chandra archives for HETG data. The retrieved spec­tra were treated in the standard way using the CIAO software (vs. 3.2.1) and corresponding threads. We have then used TITAN to model the obser­vations and to constrain the physical conditions of the WA gas in NGC 3783.

We have calculated a grid of 16 constant total pressure models dedicated to fit the WA in NGC 3783; the 16 models cover the combinations between

53

*-%. N H C O T " 2 )

Figure 1. Temperature profiles for the 3 clouds in N2003 (left) and for our WA (right) described by a single medium in total pressure equilibrium (solid line; note that the temperature stratification arises naturally); we also show a model in constant density, for comparision (dashed line; here the temperature remains constant along the medium).

S f lc-06

j

-!

! -| -! -

..... o4 05 06

— 07 —- 08

09

\ 1

j

-_. !

i

-! -;

.-1 1

I-I le-08

lw20 le+21

l O o n " 2 )

3e+22

NH (cm2)

Figure 2. Oxygen ionizing fractions ("Oi": Oxygen ionized "i—1" times). Left panel: the "medium-ionization" cloud in N2003; only O VII and O vm contribute significantly to the spectrum. Right panel: our WA in total pressure equilibrium; all ionic species contribute to some extent to the final spectrum, justifying the wide range in ionization.

4 possible values of the ionization parameter (2000 < £ = L/nnR2 < 3500 erg cms - 1 ) and of the total column density (3 x 1022 < JVH < 6 X 1022 cm - 2 ) ; the density at the illuminated face of the cloud (%) was set to 105 c m - 3 and the turbulent velociy to 150 k m s - 1 . Our study shows that the WA can be modelled in pressure equilibrium conditions, providing a best model with £ = 2500 and NH = 4 x 1022.

This model fits the observations well, both for the continuum (reproduc­ing the overall shape up to 10 keV and the O VII and O VIII edges) and the

54

lines (high and low ionization); these are blueshifted by ~ 810 k m s - 1 . Our

results were compared to those of Netzer et al. 2003 (hereafter N2003), who

found 3 constant density clouds: a "low-ionization" (£=68, NH = 8 X 102 1 ,

corresponding to the dashed line in the left panel of Fig. 1), a "medium-

ionization" (£=1071, 7VH = 1 x 102 2 , the dash-dotted line), and a "high-

ionization" (£=4265, iVH = 2 x 1022 , the dotted line). We have studied the

behaviour of the temperature , pressure and density for both constant den­

sity and constant total pressure models. In Fig. 1 we give the tempera ture

for the 3 clouds in N2003 (left-hand panel) and for our WA (right panel),

both in pressure equilibrium (solid line) and in constant density (dashed

line). Fig. 2 shows the Oxygen ionization fraction for both cases (N2003

and WA in total pressure equilibrium).

Based in our best model results and on the object's luminosity and black

hole mass, we were able to make some preliminary estimates of physical

quantities related to the WA. Assuming n n = 105 c m - 3 , the size of the WA

medium achieves ~ 2 x 101 7 cm. In order to keep the amount of outflowing

material within reasonable limits (Mout/Mgdd < 1) the WA should be

located closer than ~ 1 0 1 8 c m (i.e. before the Narrow Line Region). Note

tha t pressure equilibrium would then correspond to a flux averaged over a

long time (work in progress).

Our work demonstrates tha t the TITAN code is well adapted to the

study of the WA in AGN and tha t the WA in NGC 3783 can be modelled

by a single medium in total pressure equilibrium; this is probably the case

for other WA presently described by multiple zones of constant density. In

addition, this work opens perspectives for the future use of the TITAN code

by a larger community, through a grid of models to be made available via

Xspec and /o r via Virtual Observatory facilities.

A c k n o w l e d g m e n t s

A. C. Gongalves acknowledges support from the Fundagao para a Ciencia

e a Tecnologia (FCT), Portugal, under grant SFRH/BPD/11641 /2002 .

R e f e r e n c e s

1. Dumont, A.-M., Abrassart, A., and Collin, S., A&A 357, 823 (2000). 2. Collin, S., Dumont, A.-M., and Godet, O., A&A 419, 877 (2004). 3. Kaspi, S., Brandt, W. N., George I. M., et al., ApJ 574, 643 (2002). 4. Netzer, H., Kaspi, S., Behar, E., et al., ApJ 599, 933 (2003). 5. Krongold, Y., Nicastro, F., Brickhouse, N. S., et al., ApJ 597, 832 (2003). 6. Behar, E., Rasmussen, A. P., Blustin, A. J., et al., ApJ 598, 232 (2003). 7. Chelouche, D., and Netzer, H., ApJ 625, 95 (2005).

A S T R O P H Y S I C A L T E S T S O F F U N D A M E N T A L P H Y S I C S

C. J. A. P. MARTINS

CFP, U. Porto, R. do Campo Alegre 687, 4169-007 Porto, Portugal and DAMTP, U. Cambridge, Wilberforce Road, Cambridge CBS OWA, U.K.

E-mail: C.J.A.P.Martins@damtp.cam.ac.uk

I describe the theoretical motivation for and possible roles of cosmological scalar fields. I then present our recent measurements of the fine-structure constant at both high and low redshift. Finally I briefly discuss some ongoing and planned work and prospects for future improvements.

The most fundamental question of modern physics is whether or not

there are fundamental scalar fields in nature. They are a key ingredient in

the s tandard model of particle physics (cf. the Higgs particle), but there is

so far no evidence for them. Moreover, Einstein gravity uses only a 2-tensor

(the metric). In recent years we have come to realize tha t the early universe

is an ideal place to search for scalar fields, if they exist at all, and there

have been some possible hints for them in various contexts.

Observations suggest tha t the recent universe is dominated by an en­

ergy component whose gravitational behaviour is quite similar to tha t of

a cosmological constant. This could be the right answer, but the obser-

vationally required value is so much smaller than what would be expected

from particle physics tha t a dynamical scalar field is arguably a more likely

explanation. The slow-roll of this field (mandatory so as to yield negative

pressure) and the fact tha t it is presently dominating the universe imply (if

the minimum of the potential vanishes) tha t the field vacuum expectation

value today must be of order of the Planck mass, and tha t its excitations are

very light5 . A further consequence of this is tha t couplings of this field lead

to observable long-range forces and time-dependence of the constants of

nature . A spacetime varying scalar field coupling to mat ter mediates a new

interaction. If the recent evidence for a varying fine-structure constant 9 is

explained by a dynamical scalar field, this automatically implies the exis­

tence of a new force. A series of space missions (ACES, /xSCOPE, S T E P )

will improve on current bounds on the Einstein Equivalence Principle by

55

56

as many as 6 orders of magnitude. These must find equivalence principle violations if the current data is correct.

In theories where a dynamical scalar field is responsible for varying OJ, the other gauge and Yukawa couplings are also expected to vary. Specif­ically, in GUTs there is a relation between the variation of a and that of the QCD scale, AQCD, implying that the nucleon mass will vary when measured in units of an energy scale that is independent of QCD, such as the electron mass. We therefore expect variations of the proton-to-electron mass ratio, \i = m p /m e ( 4 ) . The wide range of a-/i relations implies that si­multaneous measurements of both quantities are a powerful discriminating tool between competing models.

Let us begin with the current observational evidence for varying a. The state of the art is provided by Murphy et al. 20039. This uses data from 128 absorption systems in the line of sight of 68 quasars, observed with the HIRES spectrograph at Keck. The weighted mean result is Aa/a = (—0.54±0.12) x 10~5. It should be noted that the evidence for a variation is only strong beyond redshift z ~ 1, and no significant evidence is found for spatial variations. As first shown in Thompson12, the proton-to-electron mass ratio can be measured through H2 absorption lines. Recent results using this method also hint at a variation. Observations with VLT's UVES spectrograph of two sources at redshifts z ~ 2.59 and z ~ 3.02 yield6

Afi/fi = (1.65 ± 0.74) x 10-5 . We emphasize that having improved measurements of both a and fi is

extremely useful for various reasons. The simplest takes us back to dark energy. It is known that a(z) can be used to reconstruct the equation of state of dark energy. But if one also has ^(2), this reconstruction will be a lot easier, not to mention less model-dependent. This method not only complements results anticipated by hypothetical future experiments (such as JDEM and DUNE), but given reasonable expectations for forthcoming improvements in spectroscopic measurements, is easily competitive with the standard methods for dark energy equation of state reconstruction (both those using supernovae and those based on weak lensing which are superior).

There is an alternative way of measuring a, which uses emission rather than absorption lines. Specifically, this uses the [0111] emission lines at the wavelengths of 5007 and 4959 A. It is interesting to note that the first as-trophysical measurement of a was done using emission lines11, whereas the first use of absorption only came about a decade later1. Remarkably, from this point the absorption measurements completely dominated the market, and for about four decades no emission measurements were attempted. As

57

we shall see there are several reasons for this — some good ones, others not so. This situation changed very recently, and two measurements took advantage of the improving quantity and quality of large-scale structure sur­vey data. Using data from 165 quasars in the SDSS survey, with a median redshift zmed ~ 0.37, Bahcall et al. 20042 find Aa/a = (1.2 ± 0.7) x 10 - 4 . As we see these measurements are about one order of magnitude less sen­sitive that the absorption ones, and also at very low redshift. Nevertheless the method has its advantages. It is quite simple and straightforward, and the lines originate from the same excited level and are very strong (so can be observed with high S/N).

This has prompted us to try to apply it at high redshift, say z ~ 3, which is the most interesting region. Such high-redshift measurements have never been attempted before. With this in mind we have obtained 10 hours of observation time with the VLT's ISAAC spectrograph, in order to carry out a pilot study for this method. Radio galaxies and quasars were observed between redshifts 2 and 3, and the data reduction was done with a spe­cial purpose pipeline (not the VLT one). Our results3 are consistent with zero change, but show consistently high values. The significance of this is currently being investigated in more detail. As things stand, we have shown that emission lime measurements can be made at high redshift, even though the sensitivity of the method is not yet competitive with absorp­tion measurements. The method has few systematic uncertainties in the physics, and is therefore well suited for evolution studies. It is also worth pointing that our wavelength calibration is the best ever for ISAAC data, and currently good enough to detect Aa/a ~ few x 10 - 5 . Improvements will require larger samples, and we will be applying to become an ESO Large Programme in the future.

Cosmic microwave background (CMB) anisotropics provide an ideal way of measuring the fine-structure constant at high redshift, being mostly sen­sitive to the epoch of decoupling, z ~ 1100. For a number of years we have used CMB datasets to constrain a7; our most recent analysis8'10 uses the WMAP first-year data and finds, at 95% C.L. that 0.95 < adec/a0 < 1.02. It is noteworthy that temperature and E-mode polarization autocorrela­tions suffer from degeneracies in different directions, for the reasons ex­plained above. Thus combining high-precision temperature and polariza­tion measurements one can optimally constrain both variations of a and T. Planck will be essentially cosmic variance limited for temperature but there will still be considerable room for improvement in polarization. This therefore argues for a post-Planck polarization-dedicated experiment, not

58

least because polarization is, in itself, bet ter at determining cosmological

parameters than temperature .

The prospects for further, more accurate measurements of fundamental

constants are definitely bright. The methods described above and other

completely new ones tha t may be devised thus offer the real prospect of

an accurate mapping of the cosmological evolution of the fine-structure

constant, a = a(z), and the proton to electron mass ratio, /U = ^(z).

This may well prove to be the most exciting area of research in the com­

ing years. Indeed the worse tha t can happen to cosmology is the scenario

where a number of cosmological parameters are fixed by WMAP, then noth­

ing new happens until Planck comes along and merely adds one (or in some

cases maybe two) digits to the precision of each already-known parameter .

After tha t cosmology may well be dead: there will be little incentive to

pushing research further to figure out what the next digit is. However, if in

the meantime violations of the Equivalence Principle and /or varying fun­

damental constants are confirmed, then one will (finally) have evidence for

the existence of new physics — most likely in the form of scalar fields —

in na ture (which one may legitimately hope tha t Planck is able to probe)

and an entirely new era begins.

A c k n o w l e d g m e n t s

This work was funded by F C T (Portugal), through grant P O C T I / C T E -

AST/60808/2004, in the framework of the POCI2010 program, supported

by FEDER. Numerical work was performed on COSMOS, the Altix3700

owned by the UK Computat ional Cosmology Consortium, supported by

SGI, Intel, HEFCE and PPARC.

R e f e r e n c e s

1. Bahcall, J. N., et al., Astrophys. J. Lett. 149, 11 (1967). 2. Bahcall, J. N., et al., Astrophys. J. 600, 520 (2004). 3. Brinchmann, J., et al, AIP Conf. Proc. 736, 117 (2005). 4. Calmet, X., & Pritzsch, H., Phys. Lett. B540, 173 (2002). 5. Carroll, S. M., Phys. Rev. Lett. 81, 3067 (1998). 6. Ivanchik, A., et al, Astron. Astrophys. 440, 45 (2005). 7. Martins, C. J. A. P., et al., Phys. Rev. D66, 023505 (2002). 8. Martins, C. J. A. P., et al., Phys. Lett. B585, 29 (2004). 9. Murphy, M. T., et al., Mon. Not. Roy. Astron. Soc. 345, 609 (2003).

10. Rocha, G., et al., Mon. Not. Roy. Astron. Soc. 352, 20 (2004). 11. Savedoff, M. P. Nature (London) 176, 688 (1956). 12. Thompson, R. I., Astrophys. Lett. 16, 3 (1975).

G A M M A RAY BURSTS AS COSMOLOGICAL PROBES*

0. BERTOLAMI AND RT. SILVA Instituto Superior Tecnico, Departamento de Fisica

Av. Rovisco Pais, 1049-001

Lisboa, Portugal

E-mail: orfeu@cosmos.ist.utl.pt; paptms@ist.utl.pt

We discuss the prospects of using Gamma Ray Bursts (GRBs) as high-redshift distance estimators, and consider their use in the study of two dark energy models, the Generalized Chaplygin Gas (GCG), a model for the unification of dark energy and dark matter, and the XCDM model, a model where a generic dark energy fluid like component is described by the equation of state, p = up. Given that the GRBs range of redshifts is rather high, it turns out that they are not very sensitive to the dark energy component, being however, fairly good estimators of the amount of dark matter in the Universe.

1. Introduction

Recently, there has been a flurry of activity about the prospect use of GRBs as cosmological probes (for an extensive discussion see 1). In the original proposal2, it has been suggested that the magnitude versus redshift plot, could be extended to a redshift up to z ~ 4.5 via correlations found between the isotropic equivalent luminosity, Liso, and two GRB observables, namely the time lag (r;as) and variability (V). The isotropic equivalent luminosity is the inferred luminosity (energy emitted per unit time) of a GRB if all its energy is radiated isotropically, the time lag measures the time offset be­tween high- and low-energy arriving GRB photons, while the variability is a measure of the complexity of the GRB light curve. Unfortunately, these correlations are affected by a large statistical (or intrinsic) scatter. This statistical spread affects not only the cosmological precision via its direct statistical contribution to the distance modulus uncertainty, a^, but also through the calibration uncertainty given that the suitable GRB sample

"Talk presented by one of us (P.T.S.) at the XV Encontro Nacional de Astronomia e Astroffsica, Lisbon, Portugal, 28-30 July 2005.

59

60

with known redshift is rather small. In what follows we show that a rela­tively small sample of GRBs with low redshifts is sufficient to greatly reduce the systematic uncertainty thanks to a more robust and precise calibration.

More recently, a new correlation was suggested3, which is subjected to a much smaller statistical scatter. The so-called Ghirlanda relation, is a cor­relation between the peak energy of the gamma-ray spectrum, Epeak (in the v — vFv plot), and the corrected collimation energy emitted in gamma-rays, E^. This collimation energy is a measure of the energy released by a GRB taking into account that the energy is beamed into a narrow jet. Unlike the Liso — r and Lis0 — V relations, the Ghirlanda relation is not affected by large statistical uncertainties, but is dependent on poorly constrained quantities related to the properties of the medium around the burst.

Another difficulty involving GRBs is that they tend to occur at rather large distances, which makes it impossible to calibrate any relationship between the relevant variables in a way that is independent from the cos-mological model. The method that is usually employed consists in fitting both, the cosmological and the calibration parameters, and then use statis­tical techniques to remove the undesired parameters. In here, we follow a different procedure1,4. We consider a luminosity distance for z < 1.5 that is measured by SNe la, and divide the GRBs sample in two sets; the low redshift sample, with z < 1.5, and the high redshift one, with z > 1.5. Since the luminosity distance of GRBs in the range z < 1.5 is now known, one can calibrate the luminosity estimators independently of the cosmological parameters and use the high redshift sample as a probe to dark energy and dark matter models.

We have analyzed the use of these several correlations in the study of the Generalized Chaplygin Gas (GCG), a model that unifies the dark energy and dark matter in a single fluid 5 through the equation of state pch = —A/p"h, where A and a are positive constants. The case a = 1 describes the Chaplygin gas, that arises in different theoretical scenarios. If the total amount of matter is fixed, there are only two free variables, A and a, although it is more customary to use the quantity Aa = A/'p\^ instead of A. Thus, we consider two free parameters, a and As. A great deal of effort has been recently devoted to constrain the GCG model parameters (for a recent review see 6) , which include, for instance, gravitational lensing7

and cosmic topology8.

In addition to the GCG model, we also study the more conventional flat XCDM model. Likewise the GCG model, the XCDM model is also described by two free parameters, the parameter, u, of the dark energy

61

equation of state p = tup, and the fraction of of dark matter, D,m. The test of these models is particularly interesting since it is known that they are degenerate for redshifts z < 1 9 '10.

2. Variability and Time Lag as Luminosity Estimators

Our work can be divided in two parts. First, we test the calibration pro­cedure. The small sample of GRBs with measured redshifts means that at present the calibration is rather poor. We assess the gain in calibrating the relations with larger samples by generating three mock samples and by performing their calibration. We find that a calibration done with 40 GRBs will greatly improve the previous results, decreasing u^ by close to half, yielding a^ = 0.68. However, by increasing the calibration sample to 100 GRBs the resulting decrease is just marginal, suggesting that is not much of a use to consider very large calibration samples. It's worth noting that a sample of about 40 GRBs may be available in the near future, thanks to the Swift satellite. We also find that despite the large statistical scat­ter, thanks to the improved calibration, the uncertainty for this estimator becomes quite close to that of the Ghirlanda relation, that is, a^ = 0.5.

We have then examined how GRBs fared when used to constrain both models under consideration. Somewhat against our expectation, we found that GRBs are not very well suited to study the GCG model. The results for the XCDM model are more promising, however we find that GRBs are sensitive essentially to fim , and very weakly sensitive to w. The reason for these results is the redshift range where GRBs lay. We have verified that when using a sample that includes 100 GRBs with z < 1.5, the constraints on the XCDM model were much tighter, as is depicted in Fig. 1. These results were found using the minimal a^ — 0.66. This uncertainty is essen­tially due to the statistical component, and hence it cannot be reduced by better calibration or data.

We also tested the use of the Ghirlanda relations, which is intrinsically more precise. As before, we find that the characteristic feature of GRBs of having rather high redshifts makes them somewhat unsuitable to study dark energy models, even the GCG one. The results are better if one uses the Ghirlanda relations, but in what concerns dark energy models not crucially. It should be noted that data quality and statistics will greatly improve in the future thanks to Swift and HETE 2 experiments.

Nevertheless, our main conclusion is that although GRBs are poor dark energy probes, for z > 1.5, the luminosity distance is quite sensitive to the

62

11 M i i i i I I

, ~- U . ,

0.2 0.4 0.6 0.8 I 0.2 0.4 0.6 0.8 1

a* nm

Figure 1. Confidence regions found for the XCDM model. The solid lines show the 68% CL regions obtained through a sample of 100 low-redshift (z < 1.5) and 400 high-redshift (z > 1.5) GRBs, while the dashed lines show the 68% CL constraints for a sample made up of 500 high-redshift GRBs only. On the left figure, the T — Liao and V — LiSO relations have been used, while on the right one the Ghirlanda relation was employed.

dominating component at the time. For the XCDM model, this is dark

mat ter , and we find tha t the amount of dark mat ter can be remarkably

constrained. For the GCG model, on the other hand, it turns out tha t

what arises is a combination of As and a parameters, and da ta cannot

lift the degeneracy on a. Actually, this feature is encountered in various

phenomenological studies of the GCG, the only exception being on da t a

from large scale structure formation1 1 .

R e f e r e n c e s

1. Bertolami, O. and Silva, P. T., Mont. Not. R. Astr. Soc. 365 1149 (2006). 2. Schaefer, B. E., Astrophys. J. Lett. 583 67 (2003). 3. Ghirlanda, G., Ghisellini, G. and Lazzati, D., Astrophys. J. 616 331 (2004). 4. Takahashi, K., Masamune, O., Kei, K. and Hiroshi, O., astroph/0305260. 5. Bento, M. C , Bertolami, O. and Sen, A. A. Phys. Rev. D66 043507 (2002). 6. Bertolami, O., astro-ph/0504275. 7. Silva, P. T. and Bertolami, O., Astrophys. J. 599 829 (2003). 8. Bento, M. C., Bertolami, O., Rebougas, M. J. and Silva, P. T., gr-qc/0512158. 9. Bertolami, O., Sen, A. A., Sen, S. and Silva, P. T., Mont. Not. R. Astr. Soc.

353 329 (2004). 10. Bento, M. C., Bertolami, O., Santos, N. M. C., and Sen, A. A., Phys. Rev.

D71 063501 (2005). 11. Bento, M. C., Bertolami, O., and Sen, A. A., Phys. Rev. D70 083519 (2004).

- 3

B R A N E W O R L D COSMOLOGY: SNEUTRINO INFLATION A N D LEPTOGENESIS

N. M. C. SANTOS? M. C. B E N T O A N D R. G O N Z A L E Z F E L I P E

Departamento de Fisica and Centro de Fisica Teorica de Particulas,

Instituto Superior Tecnico, Av. Rovisco Pais,

1049-001 Lisboa, Portugal E-mail: n.santos@thphys.uni-heidelberg.de

Modifications to the Friedmann equation in brane cosmology can have important implications for early universe phenomena such as inflation and the generation of the baryon asymmetry. In the framework of braneworld cosmology, we discuss a mechanism for baryogenesis via leptogenesis in the supersymmetric context, where the sneutrino is responsible for both inflation and the generation of the baryon asymmetry in the universe.

Today there is a wide consensus that the early universe underwent a pe­riod of cosmological inflation, responsible not only for the observed flatness, homogeneity and isotropy of the present universe, but also for the origin of the density fluctuations. At the end of inflation, the universe must have been reheated to become radiation-dominated. Such a reheating process could occur, for instance, through the coherent oscillations of the inflaton field about the minimum of the potential. During this process, the inflaton decays into ordinary particles, which then scatter and thermalise. The right abundance of baryons must have also been created after inflation. In fact, the most recent Wilkinson Microwave Anisotropy Probe (WMAP) results and big bang nucleosynthesis (BBN) analysis of primordial deuterium abun­dance imply1 TJB = (ns — nB)/n^ = (6.1 ± 0.3) x 10~10, for the baryon-to-photon ratio of number densities.

In this talk, we present a minimal supersymmetric seesaw scenario where the lightest singlet sneutrino field not only plays the role of the inflaton but

'Presently at Institut fur Theoretische Physik, Universitat Heidelberg, Philosophenweg 16, 69120 Heidelberg, Germany. N.M.C.S. acknowledges the support of Fundagao para a Ciencia e a Tecnologia (FCT, Portugal) under the grant SFRH/BD/4797/2001.

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64

also produces a lepton asymmetry through its direct decays, during the nonconventional era in the braneworld scenario2. There are other baryo­genesis scenarios in which the braneworld modifications can have impor­tant implications, e.g., the recently proposed gravitational baryogenesis mechanism3,4,5.

Whilst theories formulated in extra dimensions have been around since the early twentieth century, recent developments in string theory have opened up the possibility that our universe could be a 1+3-surface - the brane - embedded in a higher-dimensional space-time, called the bulk, with standard model particles and fields trapped on the brane while gravity is free to access the bulk6. A remarkable feature of brane cosmology (BC) is the modification of the expansion rate of the universe before the BBN era. In the so-called Randall-Sundrum II braneworld construction7 the Eriedmann equation receives an additional term quadratic in the density6,

where Mp is the 4D Planck mass and M5 the 5D fundamental mass and we have set the 4D cosmological constant to zero and assumed that inflation rapidly makes any dark radiation term negligible. Eq. (1) reduces to the usual Friedmann equation, H <x y/p, at sufficiently low energies, p C A , but at very high energies one has H oc p. Successful BBN requires that the change in the expansion rate due to the new terms in the Eriedmann equa­tion be sufficiently small at scales ~ 0(MeV); this implies M5 > 40 TeV. A more stringent bound, M5 > 105 TeV, is obtained by requiring the theory to reduce to Newtonian gravity on scales larger than 1 mm.

We consider the scenario where three heavy right-handed neutrinos Nj, with masses Mj , are added to the usual particle content of the minimal supersymmetric standard model. We assume that the seesaw mechanism is operative in the brane scenario and gives masses to the light neutrinos, and, for simplicity, we neglect the dynamics of the heavier sneutrinos ^2,3 • We also assume that the lightest right-handed sneutrino TVi acts as an inflaton with a potential simply given by the mass term V = M\N\j2, i.e., the (chaotic) quadratic potential.

In standard cosmology (SC), the COBE normalisation of the scalar per­turbations requires an inflaton mass Mi ~ I01 3 GeV. This corresponds to an inflaton field value ~ 3Mp. These super-Planckian field values can lead to quantum corrections which destroy the flatness of the potential necessary for successful inflation. If we consider the brane modifications to the Fried-

(1)

65

,12

\ WMAP bound on r\

M5 (GeV)

Figure 1. The reheating temperature TT^ as a function of Ms for m 3 / 2 = 1 TeV as derived from the BBN gravitino constraints, direct leptogenesis and the WMAP bounds on rig and Clm-

mann equation, the COBE normalisation implies8 that Mi « 4.5 x 10~5 M5. This enables inflation to take place at field values far below Mp: one es­timates Nn « 3 x 102M5 , which, when combined with M5 < 1017 GeV (required so that inflation takes place on the high energy regime of BC), im­plies Nn < Mp. One should also notice that the inflationary observables, ns, as and rs, are well within the WMAP bounds on these quantities1.

At the end of inflation the inflaton field iVi begins to oscillate coher­ently around the minimum of the potential. If CP is not conserved, the decays of 7V"i into leptons, Higgs and the corresponding antiparticles can produce a net lepton asymmetry. We require Trh < Mi, with Trh being the reheating temperature of the universe, so that leptogenesis is driven by the decays of the cold sneutrino inflaton and the produced lepton asymme­try is not washed out by lepton-number violating interactions mediated by N\ (the case where leptogenesis is purely thermal, Trh > Mi, is not con­sidered here, but this scenario has been recently investigated in BC9,10). The lepton-to-photon ratio created is given by TJL ~ eiT r^/Mi, where ei denotes the CP asymmetry in the iV"i decays. The lepton asymmetry pro­duced before the electroweak phase transition is then partially converted into a baryon asymmetry via the sphaleron effects11. Taking into account the observational value for the baryon asymmetry, it is possible to obtain

I U

10

Direct leptogenesis bound

10

> C5

10

WMAP bound on Q

10

i n '

66

a lower bound on the reheating temperature , which is defined by assuming

an instantaneous conversion of the inflaton energy into radiation when the

decay width of the inflaton equals the expansion ra te of the universe H,

Trh > 1.6 x 106 GeV.

Another important bound in supersymmetric scenarios comes from grav-

itino production. During the reheating gravitinos can be thermally pro­

duced through scatterings in the plasma. If the gravitinos are unstable and

overproduced, their decay products could put at risk the successful predic­

tions of BBN. If they are stable particles (which is the case if they are the

lightest supersymmetric particle) the constraint comes from their contribu­

tion to the dark matter . In SC their abundance is proportional to Trh , and

constraints from BBN yield a stringent upper bound 1 2 on the allowed Trh.

In BC, however, their abundance decreases with Trh, and in this case we

obtain a lower bound on the reheating temperature .

In Fig. 1, we show the allowed region in the M5 — Trh plane, put t ing

together these three constraints, for the case m3/2 = 1 TeV. In conclusion,

for a gravitino mass in the range TO3/2 — 100 GeV — 1 TeV, we find tha t

successful BBN and leptogenesis in this framework require tha t the 5D

Planck mass is in the range M5 ~ 1010 — 101 3 GeV and the reheating

temperature Trh ~ 106 - 108 GeV.

R e f e r e n c e s

1. Spergel, D. N., et al., Astrophys. J. Suppl. 148, 175 (2003). 2. Bento, M. C , Felipe, R. Gonzalez, and Santos, N. M. C , Phys. Rev. D 69,

123513 (2004). 3. Davoudiasl, H, Kitano, R., Kribs, G. D., Murayama, H., and Steinhardt, P.

J., Phys. Rev. Lett. 93, 201301 (2004). 4. Shiromizu, T. and Koyama, K. JCAP 0407, 011 (2004). 5. Bento, M. C., Felipe, R. Gonzalez, and Santos, N. M. C., Phys. Rev. D 71,

123517 (2005). 6. Maartens, R., Living Rev. Rel. 7, 7 (2004). 7. Randall, L., and Sundrum, R., Phys. Rev. Lett. 83 , 4690 (1999). 8. Maartens, R., Wands, D., Bassett, B. A., and Heard, I., Phys. Rev. D 62,

041301 (2000). 9. Okada, N., and Seto, O., arXiv:hep-ph/0507279. 10. Bento, M. C., Felipe, R. Gonzalez, and Santos, N. M. C., Phys. Rev. D 73,

023506 (2006). 11. Kuzmin, V. A., Rubakov, V. A., and Shaposhnikov, M. E., Phys. Lett. B

155, 36 (1985). 12. Cyburt, R. H., Ellis, J. R., Fields, B. D., and Olive, K. A., Phys. Rev. D 67,

103521 (2003).

X C S - C U R R E N T S T A T U S *

P. T. P. VIANA

Departamento de Matematica Aplicada, Faculdade de Ciincias da Universidade do Porto,

Rua do Campo Alegre, 687, 4169-007 Porto, Portugal

Centro de Astrofisica da Universidade do Porto Rua das Estrelas,

4150-762 Porto, Portugal E-mail: viana@astro.up.pt

We review the current status of the XMM-Newton Cluster Survey (XCS), and present the constraints on the values of the cosmological parameters <rs, £lm and QA which we expect to obtain from XCS, through the analysis of the evolution with redshift of the number density of galaxy clusters.

1. I n t r o d u c t i o n

Clusters of galaxies are one of the most important probes of the large scale

s t ructure and overall dynamical s tate of the Universe. Their present-day

average statistical properties, and their evolution as a function of redshift,

can be used to constrain the cosmological parameters tha t most influence

the formation and evolution of large scale structures: the normalization of

the power spectrum of density fluctuations, usually given as ag - the dis­

persion of the density field on scales of 8 h~l Mpc (h is the present value of

the Hubble parameter , HQ, in units of 100 k m s - 1 M p c - 1 ) ; the tota l mat ter

density in units of the critical density, f2m; the energy density associated

with a possible cosmological constant, OA- Recently, this last quanti ty as

been often subst i tuted by flw, where w is a constant assumed to describe the

equation of s tate, w = p/p, of a possible dark energy component (w = — 1

in the case of a classical cosmological constant, A).

*Work partially supported by grant POCTI/FNU/43753/2001 of Fundacao para a Ciencia e a Tecnologia.

67

68

Unfortunately, the simultaneous estimation of cosmological constraints using data from galaxy cluster surveys has been severely hindered by the fact that such data is quite sparse beyond a redshift of 0.4, due to the difficulty in detecting galaxy clusters at such high redshifts. The XMM-Newton satellite has changed the situation in a radical way, by allowing the detection at unprecedented low levels of the X-ray flux coming from the intergalactic medium in clusters of galaxies. We are taking advantage of the sensitivity of XMM-Newton, as well as of its wide field of view, to assemble a catalogue of galaxy clusters serendipitously detected in public XMM-Newton images. This joint effort of several people, namely C. Collins (Liverpool), M. Davidson (Edinburgh), M. Hilton (Liverpool), S. Kay (Ox­ford), A. Liddle (Sussex), R. Mann (Edinburgh), C. Miller (NOAO-CTIO), R. Nichol (Portsmouth), A.K. Romer (Sussex), S.A. Stanford (California), K. Sabirli (Sussex), P. Viana (Porto) and M. West (Hawaii), is called the XMM-Newton Cluster Survey (XCS). We will first review its current status, and then show to what extent the XCS will be able to constrain cosmolog­ical parameters.

2. XCS: current status

There is a pressing need for a new galaxy cluster catalogue, of greater size, and in particular going to higher redshift, than existing ones, and with a well understood selection function. We have described1 in considerable detail how such a catalogue may be constructed through serendipitous detections of galaxy clusters in archival data from the XMM-Newton satellite. By examining the many thousands of pointings which will be made, it will be possible to build a representative sample of randomly, and hence objectively, selected X-ray galaxy clusters. A significant fraction of these will have their X-ray temperatures estimated from the serendipitous data alone. This is extremely important because the X-ray temperature is the best estimator of the mass of a galaxy cluster, and thus its knowledge enables the comparison between the observational data on the cluster abundance and the theoretical predictions on the abundance of dark halos as a function of cosmological parameters.

We are presently searching for galaxy clusters in approximately 60 square degrees of public XMM-Newton images per year (which is about 40 per cent of the sky area observed), meaning that we expect XCS to cover around 500 square degrees of the sky by 2010. The effective bolo-metric flux limit of the survey is about 2.2 x 10~14 e r g s - 1 cm - 2 , or close

69

to 0.9 x 10 - 1 4 e r g s - 1 c m - 2 in the [0.5,2] keV band. If it is assumed that <T8 = 0.8, Qm = 0.3 and QA = 0.7, then around 3130 galaxy clusters with an X-ray temperature exceeding 2 keV (8 per cent of them having a redshift above one) are expected to be detected (at the 6a confidence level), with about 27 per cent of them having their X-ray temperatures estimated with less than 20 per cent error (at the lcr confidence level) from the serendipitous data alone. However, these numbers were obtained under the assumption that the relation between the X-ray temperature of a galaxy cluster and its X-ray luminosity does not evolve with redshift. Although the sparse observational data shows this to be possible2, it seems increasingly likely that on average and at fixed X-ray temperature, galaxy clusters were more luminous in the past3. If such evolution is assumed to be self-similar then around 5110 galaxy clusters with an X-ray temperature exceeding 2 keV (22 per cent of them having a redshift above one) are expected to be detected, again with 27 per cent of them with their X-ray temperatures estimated.

The XCS has several possible uses, other than constraining the value of cosmological parameters, namely the determination of the evolution with time of the intracluster gas properties as a probe to the physics of cluster formation and evolution and of the properties of cluster galaxies as a win­dow on the processes responsible for galaxy formation and evolution, as well as the exploitation of galaxy clusters as gravitational lenses of ultra-high redshift objects.

One of the key aspects of the XCS, and essential to achieve its objectives, is the detailed characterization of its selection function, so that we can have a thorough understanding of its completeness as a function of cosmological and observational parameters, like for example the typical core radius or ellipticity of a galaxy cluster. Detailed Monte Carlo simulations are under way so as to characterize as well as possible the XCS selection function.

In excess of 4000 XMM-Newton observations have been performed as of middle of 2005, with more than 3000 already in the public domain and analyzed by our collaboration. In total, around 220 square degrees of sky have already been searched for serendipitous XCS clusters. An automated download and data analysis pipeline is in place, generating a continuously updated source list from data that falls on the public domain, and which already contains more than 50 000 sources. Wavelet based software for the identification and characterization of extended sources has been developed to cleanly separate the cluster population. Well in excess of 1500 XCS galaxy cluster candidates have been identified, with around 200 being re-detections. We are in the process of acquiring and processing optical and

70

near-infrared da ta on tens of XCS cluster candidates, so as to confirm the

presence of galaxy overdensities and estimate the cluster redshift. The set

of confirmed XCS clusters will grow to hundreds, once we star t using, in

the second semester of 2005, the 33 nights of observation at the K P N O and

CTIO tha t were made available to the XCS collaboration by the NOAO as

par t of a 3-year survey program.

3 . C o s m o l o g i c a l p a r a m e t e r s from t h e X C S

Through a likelihood analysis we were able to est imate the uncertainty

associated with the estimation of cosmological parameters using those clus­

ters of galaxies in the XCS for which we will have their X-ray temperatures

reliably estimated solely from the serendipitous da ta 4 . The likelihood cal­

culation was performed by means of a Monte Carlo method 5 , whereby 2000

realizations of the expected XCS catalogue were generated for an input

fiducial cosmological model, with the addition of Poisson noise, and then

for each realization the cosmological parameters as, £lm and 17A, were al­

lowed to vary so as to find their most probable values given each catalogue.

The input fiducial model was the concordance cosmology with f2m = 0.3

and Q.\ = 0.7, for which we assumed as = 0.8. We found tha t the XCS

will provide competitive estimates for the three most important cosmolog­

ical parameters , as, Qm and QA, enabling their joint estimation to within

respectively (at least) 5 per cent, 10 per cent and 15 per cent of their t rue

values at the 95 per cent confidence. We have also determined tha t the

expected uncertainty associated with photometrically estimating redshifts

will have a negligible impact on the constraints on cosmological parame­

ters, as long as the shape of the probability distribution associated with

the redshifts is accurately known.

R e f e r e n c e s

1. Romer, A. K., et al., ApJ, 547, 594 (2001) 2. Ettori, S., et al., A&A, 417, 13 (2004) 3. Kotov, O., Vikhlinin, A., ApJ, 633, 781 (2005) 4. Liddle, A. R., et al., MNRAS, 325, 875 (2001) 5. Holder, G., Haiman, Z., and Mohr, J. J. ApJ, 560, L l l l (2001)

D E E P R A D I O O B S E R V A T I O N S I N T H E C D F S / G O O D S F I E L D : O P T I C A L A N D X - R A Y I D E N T I F I C A T I O N S

J. A F O N S O *

Universidade de Lisboa, Faculdade de Ciincias, Observatorio Astronomico de

Lisboa and Centra de Astronomia e Astrofisica da Universidade de Lisboa Observatorio Astronomico de Lisboa,

Tapada da Ajuda, 1349-018 Lisboa, Portugal E-mail: jafonso@oal.ul.pt

Recent deep radio observations of the Chandra Deep Field South have revealed sixty-four radio sources in the central area observed by the Hubble Space Tele­scope's Advanced Camera for Surveys, as part of the Great Observatories Ori­gins Deep Survey. Optical and X-ray identifications of these sources were made using the deep images of this region. Redshifts for the identified sources are drawn from publicly available catalogs of spectroscopic observations and multi-band photometric-based estimates. Using this multiwavelength information a first characterization of the faint radio source population in this region is provided. The sample contains a mixture of star-forming galaxies and active galactic nuclei, as identified by their X-ray properties and optical spectroscopy. Seven of the sixty-four radio sources have no optical identification to zsso ~ 28 mag, with only one of these being detected in the X-rays.

1. Introduction

Understanding galaxy formation and evolution is one of the major aims in modern astrophysics. To reach this goal it is essential to obtain the deepest possible views of the Universe, and a multiwavelength approach is necessary in order to avoid biases and understand the different aspects of galaxy evolution (e.g., AGN activity, obscured and unobscured star-formation, rest-frame morphologies).

Among the deepest and more thoroughly observed regions of the sky are the Hubble Deep Field-North (HDFN) and the Chandra Deep Field-South (CDFS), regions included in the Great Observatories Origins Deep Survey

"The support of the Science and Technology Foundation (FCT, Portugal) through the research grant POCTI/CTE-AST/58027/2004 is gratefully ackowledged.

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(GOODS) which was designed to unite the deepest observations from space-and ground-based facilities. The fields have been imaged by the Hubble Space Telescope (HST), the Spitzer Space Telescope and the Chandra X-ray Observatory and XMM-Newton, which resulted in some of the deepest (when not the deepest) observations ever made at optical, infrared and X-rays. The GOODS fields are also targets of many ground-based studies using 4- and 8-meter class telescopes, providing imaging and spectroscopic data in optical and near-infrared bands. The richness and depth of data implies that GOODS will be a foundation for the study of galaxy formation and evolution over the next few years.

Deep radio observations play an important role in GOODS. Not only are they capable of detecting powerful AGN to the earliest epochs, but they also reveal star-forming galaxies independently of dust-obscuration biases to cosmologically interesting distances (z ~ 1—2). Matching the radio observations to the multiwavelength data in GOODS will allow for a range of detailed investigations to be made on these evolving galaxy populations.

Here we present an analysis of the radio population in the GOODS CDFS area. We restrict ourselves to the HST's Advanced Camera for Sur­veys (ACS) region, given the homogeneous optical/radio/X-ray coverage. Optical and X-ray identifications of the sources identified in the recent Aus­tralia Telescope Compact Array 1.4 GHz radio observations (Koekemoer et al, in preparation) were searched for, and spectroscopic or photometric redshifts assembled from publicly available datasets. Using this data, the characterization of the faint radio source population in the GOODS-CDFS field was initiated and is presented here. Throughout this work we adopt H0 = 70 kms" 1 Mpc"1 , £lM = 0.3, and QA = 0.7.

2. Multiwavelength da tase ts

2 .1 . Radio, Optical and X-ray observations

The CDFS was observed at radio (1.4 GHz) wavelengths using the Australia Telescope Compact Array (ATCA). A total of 120 hours of observations were obtained, resulting in a 1.2 square degree area field covering the CDFS to a limiting (1 a) sensitivity of « 14/zJy and a beam size of 16.8" x 6.95". Koekemoer et al. (2006, in preparation) present the observations, data reduction methods and the approach used to construct the radio source catalog. Within the GOODS ACS region, a total of 64 radio sources are found, with 1.4 GHz flux densities between 63/iJy and 20mJy.

In the optical, the HST-ACS observations of the CDFS taken as part

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of the GOODS project1 were used. The data release vl.O includes ^435^7 (S435), F606W (Veoe), ^ 7 7 5 ^ (1775) and F850LP (z85o) images and cata­logs, providing photometry of sources detected in the zsso-band. Combined -B435+V6O6+^775+^850 images were made, in order to search for faint optical counterparts of radio sources not detected in the single Z850 band.

The CDFS was observed with the Chandra X-ray Observatory2. The integration time amounts to 1 Ms, being one of the deepest X-ray observa­tions ever taken. Source catalogs from two different investigations3'2, using different data reduction and source detection methods, were searched for counterparts of radio sources.

2.2. Spectroscopic and Photometric redshifts

Spectroscopic observations of many optical sources in the CDFS have been made by several groups. To investigate the nature of the radio sources considered here, the availability of spectroscopic redshifts for the potential optical counterparts was investigated from a number of works4,5 '6,7.

Whenever possible, a photometric redshift estimate was obtained, con­sidering the COMBO-17 work8, or the GOODS optical and near-infrared investigation provided elsewhere9.

3. Source Identification and Classification

Optical counterparts of radio sources in the GOODS ACS field were iden­tified using the likelihood ratio method10. The identification of the X-ray counterparts was performed by searching the 3 a radio position error region. A full account of the procedure is given elsewhere11.

Fifty of the 64 radio sources have a reliable optical counterpart. Seven further radio sources have a lower reliability optical identification. The seven remaining sources have no optical identification. On the other hand, X-ray counterparts exist for 34 radio sources, 31 of which have reliable optical counterparts and one has no optical counterpart.

In order to characterize the identified sources, spectroscopic and photo­metric redshifts (and classifications) for optical sources in the CDFS were extracted from the works previously mentioned. Around 90% of the opti­cal counterparts considered have a redshift estimate available, with more than half being spectroscopic redshift estimates. Redshifts for the optically identified radio sources range from below 0.1 to above 3.

The classification of sources was based primarily on the observed X-ray properties (Lx and hardness ratio) and, whenever possible, on the optical

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and near-infrared spectroscopic characteristics.

4. R e s u l t s

For 24 radio sources a classification is possible based on the X-ray emission

alone. Of these, 20 have an AGN designation (4 of which are powerful

QSOs), while 4 are classified as star-forming galaxies. The X-ray counter­

par t of one radio source is identified as an ultraluminous X-ray source in a

star-forming galaxy. Six of seven radio sources with no X-ray classification

display low-ionization HII region-type optical spectrum while the seventh

displays an absorption line optical spectrum.

Overall, the proportion of faint radio sources associated with AGN X-

ray sources (30%) is significantly higher tha t the proportion (20%) of radio

sources with evidence of AGN activity previously reported1 2 on the basis

of classification by radio spectral index and optical morphology.

The 7 radio sources without optical counterpart are of particular in­

terest. A preliminary analysis of the Spitzer IRAC images of this region

indicates tha t 3 of these sources are identified at mid-infrared wavelengths.

This suggests tha t these sources may be extremely reddened active galax­

ies, while the remaining unidentified sources are extremely "radio loud",

possibly at very high redshifts. Establishing the nature of these extreme

galaxies will require looking into the infrared and (sub)millimetre windows,

as well as extending the radio spectral coverage, given the possibility of

high dust obscuration and /or high redshift of these sources. Follow-up ra­

dio observations with the Giant Metrewave Radio Telescope at 327 MHz

are currently being pursued to elucidate the nature of these sources.

R e f e r e n c e s

1. Giavalisco, M., et al., ApJ 600, L93 (2004). 2. Giacconi, R., et al., ApJS 139, 369 (2002). 3. Alexander, D. M., et al., AJ 126, 539 (2003). 4. Szokoly, G. P., et a l , ApJS 155, 271 (2004). 5. Le Fevre, O., et al., A&A 428, 1043 (2004). 6. Vanzella, E., et al., A&A 434, 53 (2005). 7. Mignoli, M., et al., A&A 437, 883 (2005). 8. Wolf, C., et a l , A&A 421, 913 (2004). 9. Mobasher, B., et al., ApJ 600, L167 (2004). 10. Sutherland, W., & Saunders, W., MNRAS 259, 413 (1992). 11. Afonso, J., et al., AJ 131, 1216 (2006). 12. Richards, E. A., et al., ApJ 526, L73 (1999).

THE NATURE OF THE OPTICALLY FAINT SUB-MILLIJANSKY RADIO SOURCES: THE VLT/VIMOS VIEW*

D. SOBRAL AND J. AFONSO

Observatorio Astronomico de Lisboa, Faculdade de Ciencias, Tapada da Ajuda 1349-018 Lisboa, Portugal

The aim of this study is to characterize the optically faint submillijansky (sub-mjy) radio population, exploring its nature and evolution, and thus to complete recent studies which have successfully done this for optically bright sources. In order to achieve this, the VLT/VIMOS was used to obtain spectra of several tens of galaxies that are part of the Phoenix Deep Survey (PDS), a multiwavelength survey based on deep 1.4 Ghz radio imaging, reaching well into the sub-100 uJy level. The analysis of the first set of observations reveal 32 sources with a secure redshift determination having optical magnitudes 19<R<24 mag. Of these, 34% are star-forming galaxies, 22% are identified as Seyfert galaxies, showing active galactic nucleus signatures, 6% have absorption lines only, and the remaining 38% show narrow lines that do not allow detailed spectral classification (mainly because they are at high redshifts, or due to spectrum with poor signal-to-noise ratio). On the other hand, the sample considered in this study clearly indicates that optically faint (R> 19 mag) sub-mJy radio sources tend to be at higher redshifts, and have fainter radio fluxes, a result which confirms indications from previous work.

1. Introduction

Below a few millijanskys, deep radio surveys reveal a population of sources (the sub-mJy radio population) significantly different from the "classical" active galactic nucleus (AGN) powered radio galaxies, typical at higher flux levels. Instead, star-formation seems to be present in a large fraction of the sub-mJy population. The interest in these galaxies has increased steadily in recent years, given the insensitivity of radio selection to one of the limiting factors on our knowledge of the galaxy evolution history of the Universe: dust obscuration. However, despite its strong potential for cosmological studies, there is still limited information on the nature and evolution of these systems, especially for the optically fainter ones. Here, we present some new results for the optically fainter sources, based on spectroscopic observations done with the Visible MultiObject Spectrograph (VIMOS) at the Very Large Telescope (VLT).

This work was supported by the Science and Technology Foundation (FCT) through the research grant POCI/CTE-AST/58027/2004.

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2. Data Reduction and Analysis

Spectra for hundreds of objects were obtained from two distinct areas of the PDS1. The data was reduced using the VIMOS Pipelme and includes spectra for 32 radio sources with 19 < R < 24 mag. A FORTRAN programme was used to determine the redshift of each galaxy and spectral line measurements were performed using IRAF. Classifications were done based on [2].

3. Results and Conclusion

The redshift (Fig. 1-left) and radio flux (Fig. 1-right) distributions of this sample clearly indicates that optically fainter (R> 19) sub-mJy sources are more likely to be at higher redshifts and be fainter at radio wavelengths than the optically brighter (R < 20 mag) ones3. Nevertheless, from the 32 optical counterparts considered, 11 (34%) were classified as star-forming galaxies, 7 (22%) as Seyfert galaxies and 2 (6%) as absorption-line systems. Twelve (38%) were not assigned a classification, due to either a high redshift or low signal-to-noise spectra. When compared to sub-mJy radio galaxies with brighter optical magnitudes3 we see that Seyfert galaxies tend to increase their relative abundance at fainter optical magnitudes. Furthermore, absorption-line systems seem to vanish at fainter optical magnitudes, while star-forming galaxies remain as the predominant population, especially for Si.4 <0.2 mJy.

Figure 1. Redshift (z) distribution (left) and flux distribution (right) for the studied sample.

References

1. Sullivan et al, ApJS 155, 1 (2004). 2. Rolla et al., MNRAS 289,490 (1997). 3. Afonso et al.,ApJ624, 135 (2005).

AMS — A MAGNETIC SPECTROMETER ON THE INTERNATIONAL SPACE STATION

L. ARRUDA, F. BARAO, G. BARREIRA, J. BORGES, F. CARMO,

P. GONQALVES, R. PEREIRA AND M. PIMENTA

LIP/IST — Av. Elian Garcia, 14, 1° andar — 1000-149 Lisboa, Portugal e-mail: luisa@lip.pt, pereira@lip.pt

The Alpha Magnetic Spectrometer (AMS) is a particle detector, designed to search for cosmic antimatter and dark matter and to study the elemental and isotopic composition of primary cosmic rays, that will be installed on the International Space Station (ISS) in 2008 to operate for at least three years. The detector will be equipped with a ring imaging Cerenkov detector (RICH) enabling mea­surements of particle electric charge and velocity with unprecedented accuracy. Physics prospects and test beam results are shortly presented.

1. The AMS experiment

The Alpha Magnetic Spectrometer (AMS)1 is a particle detector that will be installed on the International Space Station (ISS) in 2008 and operate for at least three years. A successful test of the concept was made with an experimental version flight of AMS aboard the US Space Shuttle Dis­covery for 10 days in June 1998. AMS has a large geometrical acceptance (~0.5m2.sr) and will be equipped with a superconducting magnet to de­tect charged particles (up to iron) in a large range of energy (from MeV up to TeV) and to detect gamma rays. The long exposure period of AMS in space will allow the accumulation of a large statistics of events increas­ing in several orders of magnitude the sensitivity of the proposed physical measurements.

2. Velocity and charge reconstruction in the RICH detector

The inclusion of a ring imaging Cerenkov detector (RICH) will provide AMS 02 with additional and accurate measurements of particle velocity (/3 = v/c) and electric charge (Z). RICH is composed of a dual radiator (silica aerogel with n = 1.05 and NaF), a high reflectivity lateral conical mirror and a detection matrix with photomultipliers coupled to light guides. An electromagnetic cone of radiation with an aperture angle related to the particle velocity (cos0c = ^g) can be emitted ((3 > ^) when the charged particle crosses the radiator material. The particle direction (6, cj>) is re­constructed with high accuracy from signals left on silicon planes. For the

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figure 1. At left a whole view of the AMS 02 spectrometer, and at right the recon­structed charge peaks using data from the RICH beam test at CERN in October 2003 with an indium beam of 158 GeV/nucleon.

velocity reconstruction with RICH, a maximum likelihood approach was ap­plied. The overall probability of the detected hits to belong to the expected photon pattern is computed as P{6C) = \$%- p^{r^; 0C)}, where Pi is the hit probability evaluated from its distance to the pattern (r*). The angle 0C which maximizes the function P(9C) corresponds to the best esti­mation of the emission angle of electromagnetic radiation (Cerenkov angle). Electric charge can be reconstructed from the number of radiated and de­tected photons (Ni) which is proportional to Z2 and to the length (L) of radiator crossed: Nt oc Z2AL (l - -^j Ci, where a is essentially the ring acceptance.

3. Results with the RICH prototype

A RICH prototype made of a 96-photomultipliers was tested with 158 GeV/nucleon indium ion fragments at CERN in 2003. Different types of radiators were tested as well as a reflector segment. The collected data allowed to test the velocity and electric charge reconstruction algorithms as well as the characterisation of the optical properties of the radiators.

Figure 1 shows the clear separation of nuclei up to iron. Velocity recon­struction with the same test beam data showed a velocity resolution improv­ing with the charge Z as expected, ^ = ( | ) 2 @ B2, with A = 7.8 x 10~4

and B = 7.3 x 10 - 5 . The charged resolution obtained is ~ 0.2 charge units with a systematic error of ~ 1%.

References

1. S. P. Ahlen et al, Nucl. Instrum. Methods A 350, 34 (1994). V. M. Balebanov et al., AMS proposal to DOE, approved April 1995.

2. F. Barao et al., Nucl. Instrum. Methods A 502, 310 (2003).

HISTORY OF ASTRONOMY

THE LEGACY OF SACROBOSCO: TRACTATUSDE SPHAERA

BRUNO ALMEIDA

CHC-UL, Centro de Historia das Ciencias da Universidade de Lisboa

Tractatus de Sphaera, a text devoted to elementary cosmography and astronomy, began its circulation in the first half of the 13th century. Thanks to its style and contents it became fundamental in the education of many university students throughout Europe and gave rise to an intellectual tradition that prevailed in Europe for around 400 years. Our main goal in this communication is to present the treatise and its contents. In order to understand it, we will start by giving a brief introduction on the author and on the scientific and social context of the time. In the end we will focus on the impact and tradition of this text in Portugal.

1.1. Introduction and background

Around the beginning of the 12th century, a very interesting cultural phenomenon started taking place: a rising interest in science, particularly of Greek and Arabic origins, associated with a complex translation movement from non-Latin sources. By the end of the 12th century the majority of the most important texts in astronomy, like Ptolemy's Almagest, Aristotle's works and some texts from Arab authors like Albategni, Avicenna and Averroes, were available in Europe. At the same time, European society saw the birth of the University, an institution devoted to learning and based on a community of knowledge seekers.

By the time Johannes de Sacrobosco was starting to teach in the Paris University (first half of the 13th century), common students (mainly those attending the Faculties of Medicine and Liberal Arts) had, by the rules of the quadrivium, to learn a good deal of astronomy basics. From there, one could continue to study the subject and go to the more difficult theories of planets. The next and last step, the understanding of the Almagest, was not in the range of an average undergraduate; its study was reserved to a few advanced students. It is therefore clear that teaching was not uniform, being supported by complex and disperse information of which, the variety and difficulty of all the up cited documents are good examples. There was a need for texts that could explain astronomy and cosmography in an introductory and organized way - in a word there was a need for pure textbooks. It is at this point that Sacrobosco makes his entrance in the History of Astronomy.

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1.2. Biographical notes

The information about the author of the original manuscript is scarce. As Olaf Pedersen points, "one thing which we know for certain about Sacrobosco is that (in the words of Zacharias) is name is John"3. We do not know when he was born or deceased, but he surely lived in the first half of the 13th century.

According to the medieval habit, the Latin epithet "Sacrobosco", or the English equivalent "Holywood", should indicate the place where one was born. In Johannes' case this gives origin to three main hypothesis of birthplace -England, Ireland and Scotland - that still prevail today.

Regarding his college education, the most feasible hypothesis is Oxford, followed by a move to Paris. He must have died in this city after a life dedicated to teaching. Other than the Tractatus de Sphaera, he produced important works mainly concerned with mathematics - Computus and Algorismus - that also had relevant impact at the University level.

1.3. Sources of the Sphere

Many of the ones that made commentaries on the Sphere, refer to Sacrobosco as "the compiler" because the Tractatus does not present almost any new scientific achievements being based on a collection of general knowledge facts about the cosmos, much of which were a product of earlier works.

The main sources supporting Sacrobosco's work - a statement based upon inspection of the surviving manuscripts1 - must have been Alfraganus' Rudimenta Astronomica, Ptolemy's Almagest and also Macrobius' commentaries on Scipio's dream. An analyse of the Sphaera's list of citations also shows that Sacrobosco knew, at least, works of Alfraganus, Almeon, Aristotle, Eratosthenes, Euclid, Ptolemy, Theodosius, Macrobius and Pseudo-Dionysius regarding astronomical and cosmological issues. In addition, his writing and teaching style provide etymologies and offer scraps of ancient history, making use of quotations from literary texts from Ambrosius, Lucanus, Ovid, Vergil and even the Bible, most likely with pedagogical purposes.

2. Division and contents of de Sphaera

The Treaty of Johannes de Sacrobosco was, no doubt, one of the greatest landmarks in scientific literature of all times. In the words of Lynn Thorndike, this "was the clearest, most elementary, and most used textbook in astronomy and cosmography from the thirteenth to the seventeenth century"1.

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De Sphaera was originally written in Latin, in an informal descriptive style, meaning that Holywood followed a literary line close to the one of Alfraganus or Martianus Capella's books setting it apart from the complicated mathematical texts of Ptolemy or Geber. For a beginner college student (with an average age of fourteen or fifteen years old), with a low cultural background acquired at a grammar school, this work was an excellent way to start studying the subject.

The Tractatus de Sphaera is divided in four chapters headed by a small introduction in which the author points out to the contents of the manuscript.

In the 1st chapter the sphere is defined. Earth's constitution and division are described, assuming its sphericity and its central and punctual place in the Universe (according to Aristotle's philosophy) and it ends with a measure of Earth's circumference and diameter. Sacrobosco also addresses the problem of the number of celestial spheres - he adopts nine instead of the usually assumed eight, in order to give a better account of the movements of the skies.

In the 2nd chapter the main circles of the celestial sphere are described in detail: those being the equator, the zodiac, the ecliptic, the colures and the meridians. Some important small circles are also taken into account: the horizon, tropics and polar circles. In this chapter, Sacrobosco sets the definition of Artie circles that we still use today.

In the 3rd chapter some of observable consequences of the theories proposed in the two first chapters are expressed. It begins with the rising and setting of fixed stars and related phenomena, followed by an account of the variation in the length of daylight for observers at different geographical latitudes. Finally, he pays detailed attention to the question of the habitable world and to the different climata (climates)".

The sphere ends with a chapter where some elements of the theory of planetary motion are described. Sacrobosco briefly refers to Moon and Sun eclipses and comments on the much debated question of whether the eclipse occurred at the time of the Passion of Christ was a miracle or a natural phenomenon. This last chapter can reveal an intention of making a connection with the Ptolemaic models described in more complex astronomical treaties.

3. A note on commentators

The commentaries were personal notes, many times scientific, sometimes to clarify unproved passages of the original, to point out errors or to propose improvements. The amount of commentaries to the Sphere, that originated an

a We call climate to the space between successive parallels that have a difference of half hour in its longest day.

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important intellectual tradition, shows that this was an extensively studied text. This tradition included, among others, the names of Michael Scot, Robert Anglicus, Cesco d'Ascoli, Pedro Nunes, Elie Vinet and Christopher Clavius.

The Sphere was also a largely published book. In fact, it was the second ever published scientific book (Ferrara in 1472) and had 25 editions alone in the 15th century.

4. The Sphere in Portugal

The first known Portuguese edition of Sacrobosco's treatise dates approximately from 1509 (included in a nautical regimentb) and there is only record of one previous manuscript, most certainly dating from some years before 1500. Naturally, this doesn't mean that the Tractatus was not known in Portugal before that, an unawareness that would be very untypical. Across the 16th and 17th

centuries the cosmographical teachings contained on de Sphaera are incorporated in almost all Portuguese nautical Regiments.

Men like Joao de Castro and Pedro Nunes also made versions of this medieval text, both in Portuguese. In Nunes' Tratado da Sphera, printed in 1537, he presents 26 marginal notes on Sacrobosco's text - from which we highlight his «Annotatio in extrema verba capitis de climatibus», or observations to the climates chapter. This particular note, on which for the first time, Nunes makes use of trigonometry and geometry to explain the division lines of the different climates, enjoyed large reputation thanks to its inclusion on Elie Vinet's edition of the Sphere.

Acknowledgments

I am grateful to Prof. Dr. Henrique Leitao (CHC-UL) for introducing me to the study of this important text and for his constant help.

References

1. Lynn Thorndike, The Sphere of Sacrobosco and Its Commentators, (Chicago: University of Chicago Press, 1949).

2. Luis de Albuquerque, Revista da Faculdade de Ciencias da Universidade de Coimbra, 28 (1959) 142 - 176.

3. Pedersen, Journal for the History of Astronomy 16, 3: 175 — 221 (1985). 4. Pedro Nunes - Obras, Vol. I, (Lisboa: Fundacao Calouste Gulbenkian,

2002).

b This regiment is known as Regimento de Munique.

ASTRONOMICAL AND GEOPHYSICAL ACTIVITIES IN RIO DE JANEIRO (BRAZIL) DURING 1781-88

BY BENTO SANCHES DORTA

J. M. VAQUERO

Departamento de Fisica, Universidad de Extremadura, Escuela Politecnica Cdceres, E-10071, Spain

R. M. TRIGO

Centro de Geofisica, Universidade de Lisboa, Campo Grande, Ediflcio C8, Piso 6 Lisboa, J 749-0] 6, Portugal

M. C. GALLEGO

Departamento de Fisica, Universidad de Extremadura, Facultad de Ciencias Badajoz, E-06071, Spain

We summarized the works realised by Bento Sanches Dorta, a Portuguese Royal Astronomer who went to South America to perform a great number of astronomical and geophysical observations during the period 1781-1788.

1. Introduction

Bento Sanches Dorta was a Portuguese Royal Astronomer who went to Brazil to perform a great number of astronomical (e.g. eclipses, solar astrometry, occultation of Jupiter satellites ...) and geophysical (e.g. geomagnetic declination, auroras, meteorology) observations [1] during the period 1781-88. We summarized his more relevant works on astronomy and geophysics.

2. A "lost" sunspot observation

The reconstruction of the solar activity during some years of the 18th century is poorly known because there are scarce sunspot observations. Vaquero et al. [2] presented a "lost" sunspot observation realized by Dorta during his observation of the solar eclipse of 1785 from Rio de Janeiro (Brazil). This record was not included in the database compiled by Hoyt and Scharten [3].

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3. Geomagnetic measurements

Vaquero and Trigo [4] have compiled a relatively extensive catalogue of geomagnetic declination measurements performed by Dorta in Rio de Janeiro (Brazil) between 1781 and 1788. All the information was retrieved from printed documents compiled in the first three volumes of the Memories of the Portuguese Royal Academy of Sciences. During this period, Dorta performed roughly 20000 individual observations, however only a fraction of this data is presently available.

4. Meteorological observations

Sanches Dorta recorded several meteorological variables from Rio de Janeiro: temperature, pressure, rainfall, etc. (figure 1). There are very few meteorological observations of the South hemisphere during the 18th century.

1780,00 1781,00 1782,00 1783,00 1784,00 1785,00 1786,00 1787,00 1788,00 1789,00

Year

Figure 1. Monthly averages of temperature in Rio de Janeiro between May 1781 and May 1788.

Acknowledgments

J.M. Vaquero was partly supported with a grant by the Gulbenkian Foundation and Biblioteca Nacional de Lisboa.

References

R. de Carvalho, A Astronomia em Portugal no seculo XVIII, Lisboa (1985). J. M. Vaquero, R. M. Trigo and M. C. Gallego, AN 326, 112 (2005). D. V. Hoyt and K. H. Schatten, Sol. Phys. 179, 189 (1998).

1. 2. 3. 4. J.M. Vaquero and R. M. Trigo, Ann. Geophys. 23, 1881 (2005).

COMPARISON BETWEEN MONTEBRO DA ROCHA AND WILHELM OLBERS' METHODS FOR THE DETERMINATION

OF THE ORBITS OF COMETS

FERNANDO B. FIGUEIREDO

FCT - SACSA, Universidade Nova de Lisboa, Portugal E-mail: fernandoflgueiredo@netvisdo.pt

JOAO FERNANDES

Observatorio Astronomico de Coimbra

In 1797, under von Zach sponsoring, Wilhelm Olbers published his work on the determination of the parabolic orbits of the comets - "Abhandlung tiber die leichteste und bequemste Methode, die Bahn eines Cometen aus einigen Beobachtungen zu berechnen von Wilhelm Olbers". Over the next century, this method would become the main tool to determine comets' parabolic orbits. Two years later, in 1799, an article of Monteiro da Rocha entitled "Determinacao das Orbitas dos Cometas" is published in Mem6rias da Academia Real das Ciencias de Lisboa. This study publishes a method to solve the problem of the determination of comets' orbits very similar with the one proposed by Olbers. In the current article we intend to provide some information about the method of Monteiro da Rocha, which in fact was formerly formulated circa 16-17 years in advance to Olbers method, and to present the results of the quantitative side-by-side comparison of methods.

Along the 18th century, one of the most difficult questions occupying many astronomers and mathematicians was the problematic of the determination of the orbits of comets. This was an old subject, from the time Newton's published a rather ingenious method in his Principia, in 1668, tough with fairly challenging application. It was using this method, with minor adaptations, that Halley determined the orbits of 24 comets, concluding that the 1531, 1607 and 1682 comets displayed identical orbits. This led him to suggest that those events corresponded in fact to the successive and periodical transit of the same comet, due to return in 1758. Such conclusions were published in his famous work Astronomie Cometicae in 1705, giving way for the comet to be named after him.

However, the problem of the determination of the orbits of the comets remained unanswered for many years, and was addressed by many famous

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astronomers such as Euler (1707-1783), Condorcet (1743-1794), Boscovich

(1711-1787), Prosperin (1739-1803), Lalande (1732-1807), Lagrange (1736-

1813), Laplace (1749-1827) and others.

In 1772 the Berlin Academy of Sciences proposed a prize to be awarded in

1774 to the discoverer a simple method to determine the parabolic orbit of a

comet using only 3 observations. This award was only granted in 1778 to

Condorcet and Tempelhoff. Nevertheless, it was Olbers who got the historical

credit as the inventor of a simple and easily applicable method - ,4AA<3Ha7MHg

M^er a?e /e/cA ay/e HMa* Ae<yMem.yfe Me?Aoae, a7e BaA?? swas Cc/we^gH aM^ e/n;gen

BeoAacA?MHgeH ZM AerecA??e?? vow P%7Ae//M O/Aers"" which was published in

1797 under the sponsorship of Baron von Zach.

In 1799, Monteiro da Rocha published the memory in the Memories of the

Royal Academy of Sciences of Lisbon 'Determinacao das Orbitas dos

Cometas'*', where he proposed a method to solve the problematic of the comets'

orbits. This work of Jose Monteiro da Rocha is frequently cited, by Portuguese

historians of science, as one of his greatest scientific contributions:

"fAe worA ?Aaf CM/?;'v<2fe<3f Aw greafe/* f!o?or;ei!y was AM Mewory OM ?Ae ae?srwwaf?'oM q/7Ae orA/M q/cowew (.J fAe/voA/e/M wayp/*oc^'ca/(y so/vea*,yo/* /Ag_/?^^ ^'we, Ay fAe wa^Ae/wa^'c/an O/Aers, w 77^7 [this date is wrong, the correct date is 1797], accorawg fo a we/Aoa* wear(y cowc;ofew7 w;7A Ae owe Ay Afo^yg/ro aa 7?ocAa, wAojg A/ewory pMA/wAea* w;YA /arge ae/qy Ay /Ag ,4c<26?g7wy q/ ^c/e^ces q/ ZMAon on(y ;'w 779P, /ea* A;'w ?o /ooye, pr;'or/iy /w ^Ae as^aA/MAweM? q/* Ae new we^Aoa"' [1]

"however 7AM proceyy [Olbers], Aa^ Aecawe a c/ass/c, a*oes Mo/ a7/j&r esyen/;'a/(F yroTM /Ae one coM/awea* w /Ae wewo/y q/"Afon e;'7*o &? 7?ocAa (.. J [2]

" It was transited and published some years later, by the Royal Institution of London, in The Quarterly Journal of Science, Literature, and the Arts - n ej^oy on ;Ae eaj;e^; a/M/ mo.s; conven;en/ me^no<^ o/" ca/cM/a?;ng ^ne oro/f o/ a come; yrom oo^erva^on^. Ry f;7/;aw 0/oer.s, M D . vo. Ws/woy, /7P7. 7)*aH.s/afe6fyro?H German, w/^n o^^; vols. 9-13, 1820-22 [no. 9, pp. 149-162 (1820); no. 10, pp. 416-426 (1821); no. 11, pp. 177-182 (1821); no. 12, pp. 137-151 (1822); no. 13, pp. 366-385(1822)]. ^ The Memory - DeterminacSo das Orbitas dos Cometas (Determination of the Orbits of Comets), was published in volume II of Royal Academy of Sciences of Lisbon, in 1799, pp. 402-79. However, this work was first presented and read by Monteiro da Rocha to the Academy much earlier, namely in 27th January, 1782. Inclusively there is a letter, dated 17th July 1780, from Monteiro da Rocha to the Secretary of the Academy of Sciences of Lisbon where, in addition to expressing his contentment for the creation of the Academy, he reveals his interest to collaborate. Concurrently he informed the Secretary of his work on the orbits of comets, sending enclosed the three baseline equations of his method.

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The source of these quotes is the study by Duarte Leite entitied: PoM/*

/7?Mfo;'re aa /a aa/er/K^a^'on afey or^;Yg^ co/we o/'ra [3]. In this article the

author presents a brief comparison among the two methods, concluding that

both are supported in the same principles. The only difference, he wrote, is

found in the approximate reiations between two of the geocentric distances

proposed by each of the methods.

"/a .saM/e oT^ereMce eyyen^'e//e e?#ra /a? aaMX weiAoaay re^/aa J a w /a$ JeMX re/a?/on^ opprocAee^ e???7*a ofem: a*e o*M <3Mce geocen?r;'aMa^ (.. J , /a we^Aoag ;'wag/Mge par /' a^^o^o/we por^MgaM repose .sw /e^ wawas- prwc/pey a*o/?/ 'ay? e/*v/ O/Aer^, (..J aoM;aMa w o ; w cowwoae a//e co^afM// ?OMfe /ofy, Mrawgn? e/ ^a^^ /rop a"e^br;, OM ^M? propose (...) ; /a^br/MM/a a*a /a.s'^ro^owapor^MgaM a , JoMc, <2M wow^precMa aMa ce//a a"0/Aary" [4]

ActuaHy the differences between two methods !ie in the fact method of

Monteiro da Rocha uses: 1) an approximate retation between the geocentric

distances of the middle position and the terminal position of the comet; 2) the

equation of Euler-Lambert not in its habitual form, but the one obtained by

squaring the two members of the theorem. O n the other hand the method of

Olbers is characterized by the employment of: !) an approximate relation

between the geocentric distances of the terminal positions of the comet; 2)

straight application of the theorem of Euler-Lambert.

In this presentation we intend to extend the former study of Duarte Leite, raising

it to a quantitative platform. For this purpose we will apply the two methods to

the determination of the orbit of two known comets: the comet of 1769 (comet

that Olbers has used as example) and the comet of 1863V (whose orbital

parameters had been calculated by James Watson in his book on comets' orbits

[5]). The results obtained were:

Table ] - orbital elements for the comet of [769

Method of Monteiro da Rocha

- perihelion distance: 0,10873 - longitude of perihelion:147° ]' 13" - instant of perihelion passage: 7 October 3h 7m. - longitude of the ascending node: 175°49' 19" - inclination of the orbit: 43" 16' 31"

Method of Wilhelm Olbers

- perihelion distance: 0.11782 - iongitude of perihelion: 149° 53' 4" - instant of perihelion passage: 7 October 1 Oh 22m - tongitude of the ascending node: 175° 18'7" - inclination of the orbit: 41" 21' 3 0 "

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Table 2 - orbital elements for the comet of 1863V

Orbital elements

- perihelion distance: - longitude of perihelion: - instant of perihelion passage: - longitude of the ascending node: - inclination of the orbit:

Method of Monteiro da Rocha • 0,777129; • 305° 0'16,2"; •28 Dez 1863, 8:13h;

• 60°29'23";

• 65° 16'28,5";

Method of Wilhelm Olbers

• 0,7313995; • 305° 04'55,8"; •28 Dez 1863,

20: 25h; • 64° 24'6,0";

• 63° 43' 25";

according to the calculations of Watson; •0,771574; •304° 43' 11,5"; •27 Dez. 1863,

13:33 h; •60° 23' 17,8";

•64° 31'27,7"

From the values displayed above, it is evident that the method of Monteiro da Rocha succeeds, since it enables the determination of the orbit of a parabolic comet using only three observations. Moreover, the method by Monteiro da Rocha has a high level of precision which when compared with Olbers method, produces equally precise results. The relative differences between the values of Monteiro da Rocha and those of Watson do not exceed 1%, except for the instant of the transit across the perihelion; the relative differences between the values of Olbers and of Watson are even larger: 5% in perihelion distance and 7% in the longitude of the perihelion.

In fact, the results obtained when we apply the method of Monteiro da Rocha to the determination of parabolic orbits of comets are fairly consistent and present a high degree of precision. These results strengthen the conclusions of the study of Duarte Leite and provide more support to his assertions. In face of these results, we are compelled to agree with the comment of Gomes Teixeira: "The names of Monteiro da Rocha and Olbers must therefore appear together in the history of Astronomy, as the first inventors of a practical method for the determination of the parabolic orbits of Comets" [6]

References

1. Romulo de Carvalho, A Astronomia em Portugal no seculo XVIII, p. 85. 2. Francisco Gomes Teixeira, Historia das Matemdticas em Portugal. See from the same author Doutor Monteiro da Rocha, In Revista da Faculdade de Ciencias da Universidade de Coimbra (1934), IV, 192-202. 3. Leite, Duarte, "Pour l'Histoire de la Determination des Orbites Cometaires", in

Anais da Academia Politecnica do Porto, X 2 (1915), 65-73. 4. Duarte Leite, Pour I'histoire..., p. 66 e p. 70. 5. James C. Watson, Theoretical astronomy relating to the motions of the

heavenly bodies, (New York: Dover Publications, Inc; 1964). This book was first published in 1868 by J. B. Lippincott and Company.

6. Francisco Gomes Teixeira, Historia das Matemdticas em Portugal.

THE 1870 PORTUGUESE SOLAR ECLIPSE EXPEDITION -A PRELIMINARY REPORT

V. H. BONIFACIO AND I. MALAQUIAS Departamento de Fisica, Universidade de Aveiro,

3810-193 Aveiro, Portugal

E-mail: vb@fis.ua.pt, imalaquias@fis.ua.pt

J. M. F E R N A N D E S

Departamento de Matemdtica, Universidade de Coimbra, Largo D. Dinis, 3000 Coimbra, Portugal

E-mail: jmfernan@mat.uc.pt

The moon's shadow of the solar eclipse of 22 December 1870 crossed the southern part of Portugal. Seizing this opportunity to acquire both know how and state of the art equipment in the new field of astrophysics all the Portuguese astronomical and meteorologic observatories co-operated in the organisation of an expedition to the Algarve province to observe the solar eclipse. The planning, objectives and results of the expedition will be summarily outlined.

1. A new research technique

The birth of astrophysics is already well documented for the leading players of the field. The adaptation of peripheral scientific institutions to the new branch of astrophysics is less well known.

The start of astrophysics is usually connected with the work devel­oped by Kirchhoff and Bunsen, which provided an explanation to the dark absorption lines observed in the solar spectrum since Wollaston in 1802. Kirchhoff in a series of articles published between 1861 and 1863 identifies several chemical elements present in the solar atmosphere and presents his famous solar map. This fed into a renewed interest in the sun due to an in­crease observation of solar eclipses, and related phenomena (protuberances, corona) in the second half of the nineteenth century. In 1868 during the total solar eclipse of 18 August the two strands of research finally met and spectroscopic observations during totality were carried out.

It must be said that the new field of spectroscopy was viewed with some

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suspicion by the established observatories already overworked in their duties of positional astronomy. The field of astrophysics was then open and lead by amateurs, namely in England and the United States of America, work­ing outside standard practices and using either their own private incomes or donations by wealthy patrons. There were exceptions, the paramount being perhaps the Jesuit Angelo Secchi who turned to astrophysics as an expedient to use redundant positional astronomical equipment to some sci­entific useful purpose and in the process become one of the new field most influential scientists.

2. The Por tuguese Observatories

There were three public funded observatories working in Portugal between 1860 and 1870. The Royal Navy Astronomical Observatory badly located and chronically under-equipped was slowly fading away. It was extinct in 1874. The foundation stone for new and opulent Royal Astronomical Ob­servatory in Lisbon was laid in 1861, the building progressed slowly and by the end of the decade the first observations were being made. The Coimbra Observatory, created in 1772 (building completed in 1799) and managed by the Faculty of Mathematics of the University pursued regular astromet-ric work. Its main activity, besides teaching practical astronomy, was the publication of the Coimbra Ephemerides (first published in 1802) even if the instruments did not match the aspirations of the well informed Coim­bra astronomers and mathematicians during the majority of the nineteenth century.

In 1870 there was not in the country neither equipment nor expertise in doing astronomical spectroscopic work which might be surprising since the use of spectroscopical techniques was already taught in the Coimbra University. On the other hand enlightened amateur astronomers did not make any special impact in the Portuguese astronomy at the time.

3. The Portuguese Solar Eclipse Expeditions

In the recent past the Portuguese had send an expedition to observe the solar eclipse of 18 July 1860 in Spain. From the words of Rodrigo de Sousa Pinto, the expedition leader, we can gather that the expedition was some­what hastily put up. Being classically equipped there were not any relevant contributions made by Portuguese astronomers. By contrast using the new photographic technique Angelo Secchi and Warren de la Rue, working inde­pendently, unequivocally determined the solar origin of the protuberances.

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The Coimbra Ephemerides for the year 1870, published in 1868, calcu­lated the local circumstances of the solar eclipse of 22 December for a few Portuguese towns, including Louie, Monchique and Tavira inside the path of totality.

On the 27 October 1869 meeting of the teaching staff of the Faculty of Mathematics of the Coimbra University an internal commission was ap­pointed to plan the observations of the eclipse and simultaneously elaborate a document pressing the case for the government support of them.

Avoiding past mistakes was clearly an underlying concern in the plan­ning of the eclipse expedition of 1870. Contacts were immediately estab­lished by the commission members with foreign astronomers asking for advice regarding the up-to-date scientific work which was to be carried out. It is known that at least father Secchi responded. The director of the Coimbra Observatory, R. de Sousa Pinto, was also consulted and made his own observational proposal. On the 15 November 1869 the government asked the Coimbra University Principal to appoint a joint Mathematical and Philosophy faculties commission to plan an eclipse expedition. As a consequence the previous Mathematical commission was dissolved.

A detail proposal was presented by the commission on the 15 January 1870 and was basically the blueprint of the entire endeavour. The main points of it being:

• a break with tradition — the focus shifted from the classical ob­servations of contact times made with the purpose of correcting the astronomical tables to the physical observation of the luminous phenomena, observations by which the physical constitution of the sun might be ascertain according to the commission;

• an effort to make scientific relevant observations — implying that the observers should have access to the most modern instruments available;

• a concern with optimising the scarce funds for science available — only the instruments strictly necessary would be bought and only if they didn't exist somewhere else in other Portuguese institutions.

Two other government appointed commissions followed. As time went by the number of Portuguese scientific institutions involved in the expedition work increased from one to five.

Several political upheavals threatened the expedition project. Sal-danha's military coup d'etat (19 May-19 August) did not, to our knowledge, had any major impact. On the other hand the spectroscopes ordered to

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the French maker Hoffmann were not delivered on time due to the Franco-Prussian war (9 August 1870-28 January 1871). Substitutes were ordered from Germany and an improvised one was assembled at the Lisbon Indus­trial Institute. The delayed instruments provided an extra support to the idea of sending abroad a person to acquire spectral observational skills. With government backing Antonio dos Santos Viegas, physics professor at the Coimbra University went to Rome to study with father Angelo Secchi in the summer of 1870.

Surprisingly the financial support by the Portuguese government was generous. It amounted at least to half the 2500 poundsa provided for the two international British expeditions to Algeria and Italy.

In the days preceding the eclipse with all the equipment and person­nel in place, tests were conducted to establish the routines to be executed with necessary military precision during the brief minutes of totality. Pho­tographs of the Moon and the Sun were then obtained.

The bureaucracy, the logistical difficulties, the Franco-Prussian war, the Saldanha's coup d'etat, one or two mishaps did not manage to derail the expedition. Unfortunately it was not possible to control the weather. On the 22 of December it rained. We can only guess the bitter disappointment that followed. The unfavourable weather conditions plagued several other observing stations located elsewhere conditioning the results obtained. The most important outcome being arguably the observation, by Young, of the reversed spectrum of the lower solar atmosphere.

The reasons might be unrelated but after the 1870 solar eclipse expedi­tion failure we are not aware of any major Portuguese astrophysical work made during the nineteenth century.

A detailed account of the expedition will be presented in a paper cur­rently in preparation.

References

1. F. C. Freire, Memoria Historica da Faculdade de Mathematica, Imprensa da Universidade de Coimbra, p. 93-103 (1872).

2. E. V. Gomes and I. Malaquias, Proceedings of the 5th International Conference on the History of Chemistry, in press.

3. A. J. Meadows Astrophysics and twentieth-century astronomy to 1950, Vol. 4A, O. Gingerich, Ed., Cambridge University Press, p. 3-15 (1984).

4. J. S. Ribeiro, Historia dos estabelecimentos scientificos litterarios e artisticos de Portugal, Academia Real das Sciencias (1872-1893).

aThis value excludes travel expenses. Transportation was provided by the Royal Navy.

THE SCIENCE PALACES*

JOSE DUARTE C. GORJAO JORGE

Departamento de Historia e Fenomenologia da Arquitectura Faculdade de Arquitectura da Universidade Tecnica de Lisboa Rua Sd Nogueira, Polo Universitdrio - Alto da Ajuda, 1349-055 Lisboa

The OAL is a living testimony of the European Astronomical History. The emergent museum in the edified complex will preserve, beyond architectonic inheritance, the cultural symbol that inevitable expresses the institution's identity.

1. Introduction: a museum project

Amongst the observatories built in Europe during the XIX century we can highlight the unique case of the Astronomical Observatory of Lisbon (OAL) due to the undoubtedly fact that it has not suffered any significant alterations in the edified building complex (central observatory, the garden, houses and annexes) or in the scientific and technical equipment it has housed, from its construction up until today. Being part of the European and Portuguese artistic heritage, located in "Tapada da Ajuda" (an eligible place from the landscape point of view) it is mandatory that any kind of intervention must be well thought of, planned and carried out with big apprehension.

The central building was recently restored, but the impossibility of keeping the functions for which it was originally created, the Observatory will most likely be transformed into a museum space, privileging and dedicated to the history of Astronomy. Thus, it will acquire a double status. On one hand, it will remain a living testimony of an epoch in the history of science and, moreover, practically intact. On the other hand, it will assume through the new functions a symbolic destiny, inevitably assured by our cultural universe and by the international community as well. The planned intervention is rather difficult for two reasons. In first place, we should consider that up until now, no study of any sort has been done - not even from an architectonics point of view - despite the fact that it was recently restored. In second place, the principles applicable to this kind of interventions are neither set, nor driven by known methods whose baselines are scientifically authenticated and objective, i.e. a rehabilitation category to which

Supported by Fundacao para a Ciencia e a Tecnologia through grant POCTI/HAR/48711/2002

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the building should be submitted. Consequently, there is the necessity of previously determine the intervention criteria and investigate methodologies that will support them and will allow us to revitalize a building of this importance, in the sense of becoming a museum, holder of a high patrimonial value, both architectural and scientific.

2. The Museum Subject

A comprehensive study in this area is always justifiable for the reason that the usual criteria used to support interventions of this nature do not obey the scientific approaches of architectural issues placed to the project designers in practical terms. The historic or technique with a special concern to building pathologies, are part of conventional approaching models and definition of the studied object itself. Therefore, it is necessary to guarantee that the entire conceptualization process of the investigation object is rationalized. On the other hand we should be equally conscious that any process in the path of becoming a museum contains in its logical development at least two stages.

In a first stage, the goals of becoming a museum are defined through what could be designated by the subject to became a museum: objects (of any nature), linguistic constructions, forms and shapes in and from space, time records like documents, etc... Without the constitution of the "museum subject" it won't be possible to define objectively what is to be preserved through time. In these circumstances (the absence of the constitution), it is very difficult to determine which preservation method is the most effective. However, even in cases where the constitution of the "museum subject" was possible often the preservation simply cannot be accomplished. For example, we might consider objects that are reconstituted or instruments whose exhibition are subjected to our current skills, rather than the original skills that are most likely lost, forgotten, or can no longer be translated into actions similar to the original ones, or even by the absence of correct context as in the case of the Antiquity observatories, whose functions might not be known in their totality. In the second stage we must identify what functions will support the museum itself. That recognition will always be conditioned by the resources available and by the typological selections of the building that will support the entity "museum" in what concerns the physical structures of its construction. It must be taken into account that this recognition (creation or recreation) is part of the process of "becoming a museum", i.e., from the criteria from which the "museum matter or subject" will be set out and recognized as a form to linking the content to those the museum is destined to.

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In this field, universality does not exist. A "museum" is not a "typology" in the architectural sense of the term; it is not a simple "neutral" reconstruction of the objects to be exhibited. The exhibiting act itself must result from a complex study process about the available resources (witnesses of the past existence of the objects) from which will be chosen the exhibiting materials, representative of the original objects. Implicated in this process is a set of knowledge and technical skills inexorably associated to vast disciplinary fields encompassing from Phenomenology to Applied Science, Communication, History and Sociology, Theory of Art or even Perception Psychology?

To deny this, restricting the intervention parameters to a sort of Restoration Theory and Practices or to the recuperation or rehabilitation models developed in various Revitalization Theories of different arts, techniques or sciences, becomes a mere reduction which will tend to convert a potential museum subject into an imagery substitute (although realized in more durable materials under present conditions) of the "History of the Arts and Sciences" in an epoch, configured as a representation of those objects.

Therefore, the full understanding of the OAL in its previous functions, including the infrastructures, compelled us to start a comprehensive study of the building architectural features, relating the science to the architecture, trying to understand how, originally, all the devices (technical or other) were used by the succeeding inhabitants. Only after that, it will be reasonable to establish the real nature of the museum matter or subject. In what concerns the OAL, there is an extra difficulty: it doesn't exist a typology from the architectural point of view, just like the case of the object-museum. However, the scientific drive has always found a way to provide the required technical instruments in a spatial context or organization, in what we may call an "Observatory house". How was that done?

3. Architectonics of the Main Building

The first astronomical observations (if one can call that) in pre-historical ages were made in the open. We may conceptualize the first observational tools as a "one instrument" spread in the landscape or as a "spatial mechanism" regulated by the observations' requirements: orientation, ground location in regards to the observed sky areas or relative positions to other built elements. These "spatial mechanisms" evolved into smaller instruments until they become manageable by human users. As soon as the observational techniques demanded other types of facilities and functions, the whole mechanism was enclosed inside a building.

From this point of view, the OAL building shelters another structure: the technical instrumentation of the observatory. Thus, it becomes prior to anything

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else, a kind of cocoon that protects that structure "from the rain, wind and cold" (like the popular expression illustrates). It also defines a space in which the Observatory "inhabitants" develop their activities. Moreover, the furniture itself still serves the same old functions. These "sheltering structures" where actions take place and the objects are available, become the background scenery for all rituals through which Science reassures its status and scientists perform technical operations granting identity to the building and to the institution they serve.

May the two structures, the instrumental and the building, be confused with one another? No, they may not. They co-exist and, so to say, cross each other at the definition level of the building elements, whose location could eventually interfere with the shape and functions of the instruments themselves. For example, the need to have windows and doors will not affect the form or topology of the transition spaces in rooms with instruments requiring a physical and direct contact with the outside. By the same token, very specific conditions like the necessity of massive and stable supports for instruments (e.g. telescopes whose stone pillars must reach the underground rock), will force changes on the scale or shape of the architectural elements (larger sections caused by the object's weight), that will acquire disproportional dimensions relatively to other elements (windows, circular gallery and central space). Nevertheless, it doesn't impose any revision of the room's geography or even the most faint attempt to create a different expression from the one that, in normal conditions, these elements would have. It is as though the adoption of a neoclassic model in the building's conception seemed to be natural and spontaneous. Obviously, these formal options are due to the architects' cultural mindset: beyond the need to build an institution inherited from others, but in the absence of safe typological references, these options would always serve as natural design model.

The main building of the Observatory in Lisbon is an adapted version of the Pulkova Observatory (San Petersburg). Not only the final scale appears changed but also some of the structures in Pulkova's complex were simplified or are not even present. It is on a symbolic level that the variations become significant. Confirming all this, we can verify the total absence of relationships to the place (and the imagery sense) between the exterior arrangements and the ceremonious interior.

THE ASTRONOMER/INSTRUMENT MAKER CAMPOS RODRIGUES AND THE CONTRIBUTION OF THE

OBSERVATORY OF LISBON FOR THE 1900-1901 SOLAR PARALLAX PROGRAMME

PEDRO RAPOSO

Astronomical Observatory of Lisbon Centre for the History of Science of the University of Lisbon

Tapada da Ajuda, 1349-018 Lisboa, Portugal

In 1900 the Permanent International Committee for Photographic Execution of the Sky-map promoted a comprehensive observational programme on the asteroid 433 Eros, in order to determine a new and more accurate value for the solar parallax. Although having but scarce material means, the Astronomical Observatory of Lisbon gave an important contribution to this programme. This was made possible by improvements introduced by the astronomer and instrument maker Campos Rodrigues in the instruments and observational methods then employed at the observatory. This case is presented here from the point of view of the relationship between scientists and the material culture of science.

The solar parallax, defined as the angle subtended by the equatorial radius of Earth at the Sun's mean distance, is a parameter of major importance, since it gives the length of the Astronomical Unit, i.e., the mean Earth-Sun distance. Its current value (8".794148±0".000007) was adopted by the IAU in 1976 and crowns a long quest for a definitive highly accurate value1. In the last decades of the nineteenth century, after frustrating attempts to determine an accurate value by means of the observation of solar transits of Venus and Mars at opposition, the astronomers were turning their attention to close-passing asteroids. The asteroid Eros was discovered in 1898 by Gustav Witt (Urania Observatory, Berlin) and, independently, by Auguste Charlois (Observatory of Nice). At first named 1898DQ and then numbered 433, Eros was the first Earth-approaching asteroid to be discovered. In October 1900 it would be in opposition and very close to Earth, reaching the minimum distance in December. This was seen as an excellent opportunity to make a new determination of the solar parallax, and the Permanent International Committee for Photographic Execution of the Sky-map established a temporary commission charged with the coordination of the works to be carried out for this purpose. In the meeting of the Committee held in July

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25tn 1900, it was decided that the parallax determinations of Eros should be carried out by means of micrometric, heliometric and photographic observations, in a context of cooperation between European and North American observatories, and observatories located in the Northern and Southern Hemispheres. It was also pointed out that the celestial region to be crossed by Eros should be subject to a special photographic survey, in order to determine the positions of the comparison stars. The positions of comparison stars to be used in the calibration of the photographic plates should be determined by means of meridian observations. This programme, which involved 50 observatories around the world, would lead to values of solar parallax of 8".807±0".0028 (based on photographic observations) and 8".806 ± 0".004 (based on micrometric measurements), both calculated by Arthur Hinks (1873-1945)2.

Among the many observatories that received the circulars containing the guidelines for the observations of Eros was the Royal Astronomical Observatory of Lisbon, which Director was Cesar Augusto de Campos Rodrigues (1836-1919). By the time of his admission in the personnel of the observatory (1869), Rodrigues was a navy officer and a hydrographical engineer in his early thirties, bearing a remarkable curriculum, both in engineering and strictly military trades3. Once at the Observatory of Lisbon, where a whole lot of instruments were still being assembled and settled, he found a vast field where to exercise and apply his skills regarding instrumentation matters, under the challenging demands of high-precision astronomy. Soon Rodrigues started to commit himself to the careful study of the equipments of the observatory, paying particular attention to the electro-chronographic devices and the transit instruments, specially the Repsold meridian circle. He developed new electro-chronographic devices, like a new interrupter for the clocks and a new type of electric chronograph. The entire apparatus of the meridian circle was subject to an identical process of intensive study and upgrading. The right-ascension micrometer and the reticules were modified; the objective lens was stabilized by means of a spring, and a special scale was adapted to the pointing circle to avoid preparatory calculations. The illumination of the field of view and the reticule threads was improved by means of a device comprising an iris diaphragm that allowed the observer to adjust the light intensity. A symmetrical articulated chair could be adjusted according to the position of the instrument, providing comfortable seating for the observer; and it was easily and quickly reversed, when the telescope had to be pointed to an object culminating at the opposite side of the zenith. The nadir observations were also improved in several respects; for instance, Rodrigues developed a technique to produce a very smooth mercury surface, pouring the mercury against a collar-shaped piece.

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When the first circular of the new solar parallax determination effort arrived at Lisbon, Rodrigues, as director of the Observatory, had to decide in which particular field he would contribute. It was not difficult to point the parts to which he could not. As he explained in a letter to Maurice Lowey, director of the Observatory of Paris and coordinator of the commission entrusted with the solar parallax programme, the Observatory of Lisbon had no heliometer, lacked the needed photographic equipment, the micrometer of the great refractor was not in good order, and the light gathering power of the meridian instrument was not enough to make useful observations of the asteroid4. There was only a part of the programme left and attainable: the meridian observations for the catalogue of reference stars. This would be the task to be carried out in Lisbon, along with 12 other foreigner observatories. As the observations made with the meridian circle of Lisbon, by Rodrigues and his fellows F. T. Oom and Teixeira Bastos, were handed to the Observatory of Paris, the reception was acknowledged in replies containing notes of praise for the quantity and quality of the works being accomplished at the Portuguese observatory5. The catalogue of reference stars was presented later on, in Circular no. 11 of the Astro-Photographic Conference, published in 1904. Richard Tucker (1859-1952), of the Lick Observatory, had been entrusted with the demanding task of calculating the final positions for the reference stars from about 19000 observations. The Observatory of Lisbon had contributed with the highest number of observations (about 3800), yielding the highest average number of observations per star; the probable errors of Lisbon were the lowest, both in right ascension and declination; there were no rejected observations and the weight in the final mean values was the highest3. In the same year the Circular no. 11 was published, the Academy of Sciences of Paris awarded the Valz Prize to Rodrigues, by unanimous decision. The report of the prize commission emphasized that Rodrigues had obtained high precision results in a context of material limitation. The personal incitement and dedication of the astronomer, then in his sixties, was pointed as a major factor contributing to these achievements .

The scientific results that an institution or a group of individuals can attain clearly depend on the material means available to them. If those means are scarce, they must be pushed to limit in order to produce relevant results. This

The final results were presented in two lists. The values concerning the contribution of the Observatory of Lisbon were the following: probable error in RA: ± 0S.014 (first list), ± 0S.011 (second list); probable error in declination: ± 0". 15 (first list), ± 0".14 (second list); mean number of observations per star: 5.4 (first list) and 6.0 (second list). In both lists the weight of the observations made at Lisbon was 4 (in a scale ranging from 1 to 4).

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demands the scientist to have a detailed knowledge about the parts and assembling of the instruments in order to improve them. The room for such kind of intervention seems to be restricted in contemporaneous science. "Big science" undertakings, high degrees of specialization and complex instrumentation tend to relegate scientists to the simple role of users, when they deal with scientific equipments. This was not the case in nineteenth century high-precision astronomy, in which the astronomer was supposed to be an instrument expert as well, even because there was a straight physical interaction between the scientist and the instruments, with personal sources of error adding their effects to all the remaining errors at stake. Having a practical background as a Navy officer and engineer, Rodrigues fitted the profile and improved to the maximum extent the instrumentation available at the Observatory of Lisbon. This enabled him to yield important results in the context of a major program to which, at first, the means available seemed to be overall irrelevant. But this case also illustrates how limitative the material culture of science is, even when personal abilities are not a problem: photography, the main technical "hot-topic" of the Eros program, was out of reach, and the history of the Observatory of Lisbon after Rodrigues is mainly a history of slowly decline. Its instrumentation was not upgraded, in order to become an astrophysical observatory, and in the following decades, the growing city with its lights and sources of turbulence, condemned the observational work in positional astronomy.

References

1. D. Hughes, Journal for Astronomical History and Heritage 4, 15 (2001). 2. L. Pigatto, V. Zanini, Journal of Astronomical History and Heritage 5, 141

(2002). 3. General Archives of the Portuguese Navy: Livro Mestre A, Livro Mestre F. 4. Archives of the Astronomical Observatory of Lisbon; ref. C235. 5. Archives of the Astronomical Observatory of Lisbon; ref. A502. 6. Comptes rendus hebdomadaires des seances de I'Academie des sciences

139, 1075 (1904).

THE ASTRONOMICAL OBSERVATORY OF LISBON ELEMENTS FOR THE HISTORY OF ITS ARCHITECTURE*

PEDRO MARQUES DE ABREU

Departamento de Historia e Fenomenologia da Arquitectura Faculdade de Arquitectura da Universidade Tecnica de Lisboa

Rua Sd Nogueira - Polo Universitdrio - Alto da Ajuda, 1349-055 Lisboa

This paper outlines the history of the Astronomical Observatory of Lisbon's architectural construction, from the construction initiative, throughout its project and building phases, until the beginning of its use. It also presents some insights about its architectural form and proposes an interpretation related to the monumentum 's cultural significance.

The research project "Foundations of Criteria and Principles for Museulization of the Astronomical Observatory of Lisbon1" aims to the knowledge of the architecture of the OAL in order to deduct accurately and with due respect to its pre-existence, the architectural operations and revitalization of this monument as a museum. Moreover, this reading exercise of OAL's architecture will receive a structure as to serve as a model to similar future interventions in the architectural patrimony. To accomplish this goal, two primary research paths were established through the knowledge of the object's architectural form and history. It was necessary to collect the contextual data in order to accurately interpret the data obtained in this two primary research lines. This kind of research assembles three secondary or contextual research paths, namely: the knowledge of the building's architectural theme (meaning what in fact is, architecturally speaking, an Astronomical Observatory); the knowledge of the contemporary culture (meant by the social-political, scientific, artistic and other facts) and, finally, the knowledge about the people that participated in the creation of the Observatory's architecture (committee members and architects).

1. The Building History

Our history research results are mostly based on bibliographic gatherings from publications of the construction period, from more recent ones, mainly from the

This article presents some results of the first year of work supported by Fundacao para a Ciencia e a Tecnologia, through the research project POCTI/HAR/48711/2002.

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OAL's archive, which is extremely rich in original material. They are presented here, in a synthesized way, in the following table:

Year I Committee f Architecture and Use INITIATIVE 1855

1856

1857

Filipe Folque's testimony to the Comissao de Jnquerito as Repartiqoes de Marinha where he stresses the nece­ssity of a modern astronomical observatory in Lisbon.

Recommendation to the Parliament by the Navy Depart­ment Inquiry Committee towards the construction of an astronomic observatory in Lisbon. Project-Law about the observatory to be built in Lisbon. King D. Pedro V (1837-1861) donates thirty cantos de reis (30,000). Struve reports to the Government with information regarding the construction of the Astronomical Observatory.

Contract between the Baron of Paiva (1819-1868) and Jean Colson in Paris, declaring that the architect will work for a 3 years period, in the service of the Ministry of Public Work of Portugal. The architect arrives at Lisbon in March. Feb. 14"1 Decree-Law constituting the committee responsi-ble for the construction of the Lisbon Royal Astronomic Observatory: Jose Feliciano Costa, Drs. Filipe Folque, Joao Ferreira de Campos and Guilherme Jose Dias Pegado.

The committee chooses a place for the construction of the Observatory in the Royal Tapada da Ajuda called Alto da Eira Velha. The owner, D. Pedro V donates it.

PROJECT 1859

1860

Commission of a study for the Lisbon Astronomical Observatory (study based on the design of Pulkovo). Corrections to the first study: greater monumentally, suppression of the parasol. Corrections to the second study: inclusion of parapet and increasing of the floor to ceiling height. Contract with the architect for the elaboration of the detailed design, following the second study. Corrections to the detailed design by the committee: increase of the central room radius in 44 centimetres.

Jean Colson (architect) - First study.

Jean Colson (architect) - Second study (November).

The architect Jean Colson (in Paris since July) signs (in August) the project and the design statement for the cons-truction of the Lisbon Royal Astronomical Observatory.

CONSTRUCTION WORK 1861

1863

1864

1867

1869 1870

1872

1878 1879

1881

Frederico Augusto Oom returns from Pulkovo. He's nominated to supervise the construction of LRAO.

Contract of a German company for the construction of the Spinning Tower.

The construction begins in March. The responsible for the construction is Master Jose Pedro Bento Rodrigues. FA Oom: technical guiding in the construction of necessary mechanisms and systems for the observation rooms. Jose da Costa Sequeira (architect) is believed to start following the construction of the LRAO . The construction is almost finished, except the room of the grand equatorial with the Spinning Tower. Project for the Spinning Tower of Frederico Augusto Oom and T - j .-i . o • . Fintf observalions with Ihe Easl room inslnimenl.

Jose da Costa Sequeira. First observations with the West room instrument. Visit of D. Pedro II of Brazil (he doesn't visit the upper floor)

Building's end of construction with the conclusion of the installation of the Spinning Tower. In September, Filipe Folque predicts the conclusion of the construction until de end of the year. Final conclusion of the construction. March 26 - official delivery of the central building, extensions, instruments and furniture. First documental refe-rence about housing orientation of Valentim Jose Correa. Article about LRAO in the magazine O Occidente: the Observatory is finished and operational.

2. Notable aspects of the building architecture

The understanding of the geometry and materials of the OAL's architecture turned out to be very clarifying about the project and its construction, unveiling some ideological prepositions. The form analysis was extended to the prints, drawings and design statements that explain and constitute a comprehensive

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framework. The full data set allowed us, not only to grasp some "intuitions" (we hope to get evidences for) about the architectural environment, but also to establish concrete follow up research lines, e.g., in regard to the participant architects in its construction, the genetic references of the building, its context within the contemporary cultural environment and feedback consequences.

A comparison between drawings of different stages of the project allowed us to note, for instance, a small but meaningful correction. The committee corrects Colson's detailed project, by increasing the central building radius in 0.44cm, beyond the predicted 4m. The oddity of this number leads us to question its reason: was it due to a functional cause, i.e. required by an instrument? is there a geometrical reason with esoteric connotations? We ended up verifying that this was due to a desire of absolute coincidence in dimensions between Lisbon's and Pulkovo's Observatory. Pulkovo had been constructed according to a regional measuring system: the 3 sqjene (in Russian, sazheri) of radius in the building's central room corresponds exactly to 4.44 m. This fact expresses undoubtedly a desire of affiliation between Lisbon and Pulkovo, or some sort of architectural genealogy in Pulkovo's Observatory. It is, however, an awkward affiliation. The overlapping of drawings between Lisbon and Pulkovo allowed us to verify that this coincidence was limited to the central body, the most representative one, i.e., the areas where instruments are located, have no similar relation. Thus, the building's character pretended to be functional, was denied. There are more data confirming this statement: looking at the records in the visitors' book and to old photographs we realize that from its opening, the building received a large number of non-professional visitors (e.g. ladies with children) that simply came to visit the Observatory. From the beginning it had a culturally paradigmatic character: the society of those times felt or looked to be represented by it.

3. Some Conclusions

A monument interacts at two levels with its contemporary culture: first, it is influenced by it and to a certain extent derives from it; second, it carries out a formative action of the polis mind, at a pedagogical level. In both cases it always presents itself, if truly is a monument, as an objective paradigm and symbol of the culture and society of its time. It is only through the full understanding of the dialectic relationship monument-contemporary culture that one can truly infer the being and raison d'etre of a monument's existence and subsistence, which will guides us to its appropriate and correct conservation.

One could indicate as dominant cultural traces at the final stages of the XIX century, the secularisation of society, leading to the production of substitutes for

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the old religion, among which we find Science as one of them. This fact attains

to the most relevant artistic choices of the time. Moreover, a sharp segregation

between rational thinking and other forms of sentimental or spiritual life took

place here. Compte's positivism assigns to Science and Philosophy the

transmission of rational thinking, carrying into the Arts the remaining tension of

the human spiritual activity, thus, leaving the artistic forms with an overload of

sentiments (for example, the Italian operas, Offenbach's operettas and the

appearance of the melodramatic form).

The OAL's architecture carries the synthesis of these two effects. Firstly, it

assumes itself as a temple of science: evident in its topographical situation

(similar to the Acropolis), through its own structure (made to be seen from the

outside but with successive exclusive cameras, such as those found in the Greek

and Egyptian temples) and by its own social repercussion, frequented not only by

the scientists, but also by a wide circle of profanes, simple curious people,

attracted by its grandiosity and rituals. Secondly, its architecture also manifests

the sentimental tendency characteristic of contemporaneous art. Nevertheless,

OAL's unique use does not invent a new architectural type. Quite the opposite, it

recurs to preexistent archetypes (the temple is an example), proposing in the

inside environments that refuse sophistication, rather like a traditional dwelling.

References

1. Jose Silvestre Ribeiro - O Real Observatorio Astronomico de Lisboa Noticia Historica e Descriptiva, Typographia da Academia Real das Ciencias Lisboa, 1871.

2. 2" Contrato assinado pelo Barao de Paiva e Jean Colson in Biblioteca Arquivo Historico do Ministerio das Obras Publicas, Reparticao Central 102.

3. Administrative and other (foundation) documents in the Archive of OAL. 4. Maria Calado - Quadro cronologico in Jose da Costa Sequeira - Nocoes Tedricas de

Arquitectura Civil, Breve Tratado das Cinco Ordens de Arquitectura Jacomo Barozzio de Vignola. Lisboa: Faculdade de Arquitectura, 1993.

5. Contrato celebrado para a construcao da torre giratoria do ROAL (sem efeito) in BAHMOP - Livros de Contratos (1860.04.12 a 1887.12.28 - 5 vol.) Ministerio das Obras Publicas Comercio e Industria - Reparticao Central 5 / Livro 2°.

6. J. Pereira Osorio - Sobre a Historia e desenvolvimento da Astronomia em Portugal in - Historia e Desenvolvimento da Ciencia em Portugal (ate ao sec. XX), Volume 1. Lisboa: Academia das Ciencias de Lisboa.

7. O Occidente, Revista Illustrada de Portugal e do Estrangeiro. 4° anno vol. IV - n° 96. Lisboa, 21 de Agosto de 1881.

TIME SERVICE AND LEGAL TIME IN PORTUGAL

MARINA SILVA1

Escola Secundaria de Bocage, Av. Rodrigues Manito Setubal, 2900-058 Setubal, Portugal

RUI J. AGOSTINHO

Centro de Astronomia e Astrofisica, Observatorio Astronomico de Lisboa Tapada da Ajuda, 1349-018 Lisboa, Portugal

The determination, maintenance and provision of the Legal Time to Portugal has been one of the mandatory objectives of the Astronomical Observatory of Lisbon (OAL). The goal of this paper is to reveal aspects of this history, making public the contribution to the determination and transmission of Legal Time, in a time period which spreads from the final decades of the 19th century into the first decades in the 20th century.

1. Time Service in the Astronomical Observatory of Lisbon

In the middle of the XlXth century, the determination of stars' parallaxes was vividly debated in the Paris' Academie des Sciences. A movement arose from a debate between two famous astronomers, Faye and Struve, which led to the creation of the Royal Astronomical Observatory of Lisbon RAOL.

The RAOL was planned (with the help of Fig. 1 - The Astronomical Observatory Struve) and devoted to sidereal astronomy, of Lisbon Therefore, it was equipped accordingly with the best instruments from German makers like Repsold and Merz. The Portuguese Letter Law of May 6th, 1878, establishes its Organic Law. Later regulations for its implementation (Decree of 20th June 1903) established as a secondary scientific goal the keeping of official time (through daily transit observations and pendulum clocks), and also the obligation to telegraphically transmit the official local solar time (civil time) to semaphoric stations and other places in the country. The Navy's Astronomical Observatory, on a daily basis, had previously ensured this time service.

1 This paper is based on a Master's degree thesis in "Physics for Teaching", under the supervision of Prof. Rui Agostinho

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In 1911, considering that there were "broad and doubtless advantages" the Republic's Provisional Government decreed, on May 26th, that "Legal Time in all Portuguese Republic's territory is subordinated to the Greenwich Meridian, according to the principle adopted in the Washington Convention in 1884." In this act of law, it was also decreed that time transmission was a responsibility of the same institutions which had, until then, carried it out.

-Arsenal's Time Ball

2. The Arsenal's Time Ball

Besides the telegraphic transmission to inland stations, a "time instant" visual device had been adopted in many harbours worldwide, to help ships synchronize their inboard clocks: the drop of a large ball. The service is first regulated in "Diario da Republica" (official journal of the Republic) of November 9th 1858, where an announcement states: "(...) the afore-mentioned observatory will, on a daily basis and by the drop of a time ball, indicate the rigorous instant when the astronomical clock of the same observatory shows exactly 1 p.m. (...)", from that date on.

The first time ball was located in Arsenal (in Lisbon's harbour). It was replaced in August 15th, 1885. After 27 years of use, the Arsenal's Time Ball began to present some problems, such as the lack of visibility, due to the urban growth of the city of Lisbon, and the wearing out of the equipment. In the Decree published on 19th August 1911, the Ministry of Interior designated a commission to study and elaborate the project of the new time signal of Lisbon's Harbour. This commission was made up of Navy Commander Hugo de Lacerda (President), Engineering Major Frederico Oom (Secretary) and Navy Lieutenant Augusto Ramos da Costa (Vowel). Frederico Oom (sub director of OAL) had already installed in Lourenco Marques's Harbour (Mozambique), a time signal similar to the one in Hamburg, and Hugo de Lacerda had, for long time, directed it. Augusto Ramos da Costa was the Director of Time Service in Arsenal.

On May 24th 1912, the commission, without the collaboration of Hugo de Lacerda who had taken the position of Captain of Macau's Harbour, presented a report with the results of its work. The conclusions were as follows:

Fig. 3 - Time Signal of Lourenco Marques' Harbour

the time ball drop is a signal which leaves much to be desired;

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• there are different types of signals but the majority don't present enough advantages to be generalized;

• one signal per day isn't enough for navigation needs; • there is a very complete and carefully tested system, which is sufficiently

satisfactory, already working in Hamburg and Lourenco Marques; • it's probable that wireless telegraphy system, already in use, will become

common, causing the harbour time signals to lose their importance. As a result the Commission recommended the

construction in Lisbon of luminous signals system, like the ones in Hamburg and Lourenco Marques. They consisted of:

-one or more lanterns with electric light bulbs of 100 candles with metallic filament;

-a special clock to switch it on and off, which could be used as a public clock;

-a small house where the clock would be placed with the remaining equipment.

Fig. 4 -Cais do Sodrf's Clock

3. Luminous Time Signals of Lisbon's Harbor

Fig. 5 - Lantern of luminous signals.

For the installation of the new time signal system Frederico Oom asked for the collaboration of Hamburg's Observatory Director, Richard Schorr, who offered his help. On March 30th 1915, Decree 1:469 regulated the Legal Time Service concerning a new time signal in Lisbon's Harbour. Thus, the second time ball gave the last signal at 1 p.m. on 31st December 1915, and the luminous time signals started functioning in Lisbon's Harbour the next day.

Two lanterns, one situated in Cais da Alf&ndega and the other in Junqueira, near Cordoaria, gave these signals. Each lantern had three sides. In the middle of each, a luminous horizontal line of lights turned on 5 minutes before time and turned off at the exact hour. The Cais do Sodre clock which turned the lanterns on-off was electrically synchronized with the Standard clock at OAL.

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4. Legal Time, Wireless Telegraphy and the Internet.

In October 1912 the Time Conference held in Paris decided on the adoption of Universal Time. In 1913, OAL acquired devices for the reception of radio signals emitted from the Eiffel Tower (since 23rd May 1910).

On April 21st 1917, Law n° 680 reorganized the Legal Time Service instituting a Governing Board constituted by a Director and an Associate, both the highest-ranking officers at OAL.

Decree n° 10.191, of October 17th 1924 established that a telegraphic time signal would be given by the Radio-Telegraphic Station in Monsanto (Lisbon).

Currently, the OAL still keeps Legal Time for the country, with several atomic clocks and provides it through the internet, via simple and secure NTP.

References

1. Actas da Comissao do Novo Sinai Horario do Porto de Lisboa. 2. Carta de Lei de 6 de Maio de 1878 (Lei Organica do Real Observat6rio

Astronomico de Lisboa). 3. CorrespondSncia da Comissao do Novo Sinai Horario do Porto de Lisboa. 4. Costa, M. (1956). O balSo do arsenal e o tiro da Escola Polit&nica: duas

curiosidades lisboetas. Lisboa. 5. Decreto de 20 de Junho de 1903 (Regulamento do Real Observat6rio

Astron6mico de Lisboa). 6. Decreto, com forca de lei, de 26 de Maio de 1911 (Hora Legal) 7. Decreto n° 10.191, de 17 de Outubro de 1924. 8. Lei n° 680 de 21 de Abril de 1917. 9. Relatdrio da Comissao, nomeada por Decreto de 19 de Agosto de 1911, de

24deMaiode 1912.

DOCUMENTS OF THE OAL'S ARCHITECTURE*

RITA GOMES BATISTA*

Departamento de Historia e Fenomenologia da Arquitectura Faculdade de Arquitectura da Universidade Ticnica de Lisboa

Rua Sd Nogueira - Polo Universitdrio - Alto da Ajuda, 1349-055 Lisboa

RUI J. AGOSTINHO

Centro de Astronomia e Astrofisica, Observatorio Astronomico de Lisboa Tapada da Ajuda, 1349-018 Lisboa

The recovery of historical drawings and handwritten documentation has been a powerful method to discover new data and helped to shed light on the historical context for the creation of the Astronomical Observatory of Lisbon. We show here some examples.

1. Gathering the historical documents

In the context of the research project "Scientific Foundations and Criteria for the musealization of the Astronomical Observatory of Lisbon1" (OAL) we began the work of gathering, identifying and cataloguing the dispersed drawings, blueprints and handwritten documentation related to the foundation of the OAL.

We have found about one hundred drawings related to the architecture of the OAL. The drawings were grouped by thematic characteristics for an easier indexation such as: studies for the main building, projects for the main building, studies for the large refractor telescope tower, projects for this main tower, partial drawings or details, astronomical and auxiliary instruments drawings, astronomical drawings, projects of building infrastructures, projects for the two small exterior towers, maps, projects for the dwellings, studies for the garden around and some more recent drawings. In what concerns the handwritten but related documentation we selected 165 texts, of which 115 are already studied. This allowed us to discover new data on the history of the construction of the OAL and on the participation of the "owners", architects and builders.

" This work is supported by Fundacao para a Ciencia e Tecnologia grant POCTI/HAR/48711/2002. + Work partially supported by Totta-UTL inter-escolas 2004/2005.

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2. Some Illustrations

Figinc 1 Snout1 tutl> 'oi the Royal AslioiKvsiical Obscivjluiv by k.in Colson. November 18: Archi w ol tiit. UbjU > uioi IO Asuonom.co dt Libboa.

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Figures 2 and 3. Execution Project for the Royal Astronomical Observatory by Jean Colson, August i860, (detail of the rotating tower) in Archive of the Observatono Astronomico de Lisboa,

References

1. Archive of the Observatono Astronomico de Lisboa 2. Library and Historical Archive of the Ministerio das Obras Publicas.

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2005 PAST MEETS PRESENT IN Astronomyand

Astrophysics

This volume considers recent theoretical and observational

developments in astronomy and astrophysics with contributions

on solar system bodies, extrasolar planets, star formation, galaxy

evolution and cosmology. A special section is dedicated to the

history of astronomy including papers on the history of the

Astronomical Observatory of Lisbon, time service and legal time.

the 1870 solar eclipse expedition, and a comparison between

Monteiro da Rocha and Wilhelm Olbers' methods for the

determination of the orbits of comets.

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6178 he ISBN 981-256-887-5

9 YEARS OF PUBI ISHINO www.worldscientific.com