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No. 92 – June 1998

F I R S T L I G H T

Omega Centauri, obtained with the VLT UT1 on May 16, 1998. (For more details, see text in box on page 3.)

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This colour image of a famous southern Plan-etary Nebula, the Butterfly (NGC 6302), wasobtained by combining blue, yellow and redimages obtained on May 22, 1998, with 10-minute exposures and an image quality betterthan 0.6 arcseconds.

Towards the end of their life, some low-massstars expand to giant dimensions. They shedmost of the hydrogen in their outer layers asa strong “stellar wind”, before they contracttowards a final compact stage as “whitedwarfs”. After this ejection process, the starremains thousands of times brighter and alsomuch hotter than the Sun during a few thou-sand years. Its strong ultraviolet radiation hasthe effect of ionising the previously ejectedgas, which then shines before it dispersesinto interstellar space. The resulting nebulae(traditionally referred to as Planetary Nebu-lae, because of their resemblance to a planetin a small telescope) often exhibit very com-plex morphologies.

The Butterfly Nebula belongs to the class ofbipolar nebulae, as this picture clearly illus-trates. A dark, dusty and disk-like structure –seen edge-on in this image – obscures thecentral star from our view. However, its strongradiation escapes perpendicular to the diskand heats and ionises the material depositedthere by the stellar wind.

The origin of the dark disk may be due to thecentral star being a member of a double starsystem. This has been shown to be the casein some other bipolar nebulae in which, con-trary to the Butterfly Nebula, there is a directview towards the star.

First Light of the VLT Unit Telescope 1R. GIACCONI, Director General of ESO

The VLT represents a major new stepforward for world astronomy. The newconcept of active control of a thin mono-lithic large mirror, embodied in the design,yields, even at this early stage, an angu-lar resolution among the finest everachieved in optical and infrared wave-lengths from the ground. The full reali-sation of the VLT array (which will includefour 8.2-metre and three 1.8-metre tele-scopes) will result in a combination ofarea and angular resolution which willpermit us to achieve sensitivity compa-rable or superior to any on Earth. Whenthe array is used in the interferometricmode, it will result in angular resolutionsuperior to that yet achieved in space.

This formidable new observational ca-pability will provide astronomers a newopportunity for the study of the Universe.In particular we will be able to probe thegreat questions of modern astrophysics:

• The beginning, evolution and futureof the Universe we live in.

• The formations in the most remotepast of large structures, galaxies andstars and their life cycle.

• The formation and evolution of plan-ets and of the physical and chemicalconditions for the development of life.

In each of these fields, VLT will giveastronomy new capabilities for greater in-

depth investigation and understanding,thus further enhancing the great prestigewhich astronomy is now enjoying in theworld. The combination of high technolo-gy and deep scientific and philosophicalquestions is fascinating to young and oldand to the general public, touching as itdoes on the sense of awe and wonderthat accompanies our quest for the ori-gins of the cosmos and our place in it.

For Europe this event marks the real-isation for the first time in this century ofa facility for ground-based optical and IRastronomy which equals or surpassesany available in the world.

Institutes of research and industriesfrom all European member states havecontributed to this effort which clearly ex-ceeds what any European nation couldachieve using its own resources. It wouldbe impossible to recognise each contri-bution on this very large programmewhich has extended over more than adecade and represents literally more thanten thousand man years of effort.

The VLT programme has been exe-cuted within planned schedule and cost.Even at this very early stage of evalua-tion we can state with confidence that thetechnical performance of the first of thefour identical 8.2-m telescopes meets orexceeds our expectations in all respects.

I should emphasise that while this mo-ment is very significant, it is only a be-ginning. It marks the start of operationsfor a very powerful new observational fa-cility which will be completed in 2003. Thefull scientific utilisation of VLT and VLTIwill occur over a period of at least twodecades. The new design of the tele-scopes, their truly exceptional realisationby industry and their excellent perform-ance will present the astronomers withthe challenge of taking full advantage ofthis new instrument and of inventing newways to do their research and maximis-ing its effectiveness. The enormousamount of data which will become avail-able over this period will require archiv-ing capabilities much greater than hith-erto used in astronomy. Marvellous asthis machine is, it will not hold its com-petitive edge forever, and ESO and thescientific and industrial community it rep-resents are already at work to preparenew technology for the next round of ob-servational facilities.

Finally I wish to recognise the unitedand extraordinary contributions of theESO staff in Garching, La Silla, Paranaland Santiago. This great success of VLTof which we are all so proud is due inlarge measure to your competence, en-thusiasm and dedication.

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Centaurus A is the closest active elliptical gal-axy and one of the strongest radio sources inthe sky. This image shows part of the dust lanethat obscures the central regions of the gal-axy. This complex structure is believed to bethe result of the recent collision between theold elliptical galaxy and a dwarf, gas-rich gal-axy. Intense star formation is taking place with-in the violently stirred gas during the mergingevent.

This image was taken with the Test Cameraof the VLT UT1 telescope on May 22, 1998,during a short, 10-sec exposure through a redfilter to demonstrate the large light collectingpower of the 53-m2 mirror of the VLT UT1. Itshows a wealth of fine details. The image qual-ity is about 0.49 arcsec.

The insert shows a complete view of Centau-rus A taken with another telescope. The bright-est stars are foreground objects located with-in our own galaxy, but clusters of recentlyformed stars are visible at the edge of the dustlane.

With powerful infrared detectors to be mount-ed on the VLT later this year, astronomers willsoon be able to probe deep into the dust lane,infrared light being less absorbed by dust thanred light.

The Final Steps Before “First Light”The final, critical testing phase com-

menced with the installation of the 8.2-m primary (at that time still uncoated)Zerodur mirror and 1.1-m secondary Be-ryllium mirror during the second half ofApril. The optics were then graduallybrought into position during carefullyplanned, successive adjustments.

Due to the full integration of an ad-vanced, active control system into theVLT concept, this delicate process wentamazingly fast, especially when com-pared to other ground-based telescopes.It included a number of short test expo-

sures in early May, first with the GuideCamera that is used to steer the tele-scope. Later, some exposures weremade with the Test Camera mountedjust below the main mirror at the Cas-segrain Focus, in a central space insidethe mirror cell. It will continue to be usedduring the upcoming CommissioningPhase, until the first major instruments(FORS and ISAAC) are attached to theUT1, later in 1998.

The 8.2-m mirror was successfullyaluminised at the Paranal Mirror Coat-ing facility on May 20 and was reat-

tached to the telescope tube the follow-ing day. Further test exposures werethen made to check the proper func-tioning of the telescope mechanics, op-tics and electronics.

This has led up to the moment ofFirst Light, i.e. the time when the tele-scope is considered able to producethe first, astronomically useful images.Despite an intervening spell of bad at-mospheric conditions, this importantevent took place during the night of May25–26, 1998, right on the establishedschedule.

The image shown on page 1 was obtained with the VLT UT1 on May 16, 1998, in red light (R band), i.e. while the mirror was still uncoated.It is a 10-minute exposure of the centre of Omega Centauri and it demonstrates that the telescope is able to track continuously with a veryhigh precision and thus is able to take full advantage of the frequent, very good atmospheric conditions at Paranal. The images of the starsare very sharp (full-width-at-half-maximum (FWHM) = 0.43 arcsec) and are perfectly round, everywhere in the field. This indicates that thetracking was accurate to better than 0.001 arcsec/sec during this observation.

Omega Centauri is the most luminous globular cluster in our Galaxy. As the name indicates, it is located in the southern constellationCentaurus and is therefore observable only from the south.

At a distance of about 17,000 light-years, this cluster is barely visible to the naked eye as a very faint and small cloud. When Omega Centauriis observed through a telescope, even a small one, it looks like a huge swarm of numerous stars, bound together by their mutual gravitationalattraction.

Most globular clusters in our Galaxy have masses of the order of 100,000 times that of the Sun. With a total mass equal to about 5 millionsolar masses, Omega Centauri is by far the most massive of its kind in our Galaxy.

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Superb image quality is the prime requirement for the VLT. The VLTshould take full advantage of the exceptionally good “seeing” condi-tions of the Paranal site, i.e. periods of time when there is a particularlystable atmosphere above the site, with a minimum of air turbulence.In this diagram, the measured image quality of the VLT UT1 astronom-ical images is plotted versus the “seeing”, as measured by the SeeingMonitor, a small specially equipped telescope also located on top ofthe Paranal Mountain.The dashed line shows the image quality requirement, as specified forthe VLT at First Light. The dotted line shows the specification for theimage quality, three years after First Light, when the VLT will be fullyoptimised. The fully drawn line represents the physical limit, when nofurther image distortion is added by the telescope to that introduced bythe atmosphere.The diagram demonstrates that First Light specifications have beenfully achieved and, impressively, that the actual VLT UT1 performanceis sometimes already within the more stringent specifications expect-ed to be fulfilled only three years from now.Various effects contribute to degrade the image quality of a telescopeas compared to the local seeing, and must be kept to a minimum inorder to achieve the best scientific results. These include imperfec-tions in the telescope optical mirrors and in the telescope motion tocompensate for Earth rotation during an exposure, as well as air turbu-lence generated by the telescope itself. The tight specifications shownin this figure translate into very stringent requirements concerning thequality of all optical surfaces, the active control of the 8.2-m mirror, theaccuracy of the telescope motions, and, in the near future, the fast “tip-tilt” compensations provided by the secondary mirror, and finally thethermal control of the telescope and the entire enclosure.The only way to achieve an image quality that is “better than that of theatmosphere” is by the use of Adaptive Optics devices that compen-sate for the atmospheric distortions. One such device will be operativeon the VLT by the year 2000, then allowing astronomers to obtain im-ages as sharp as about 0.1 arcsec.

In this diagram, both seeing (horizontal axis) and telescope image quality (vertical axis) are measured as the full-width-at-half-maximum (FWHM)of the light-intensity profile of a point-like source. The uncertainty of the measurements is indicated by the cross in the lower right corner.

In the VLT control room at the moment of “FirstLight”.

VLT First Light and the PublicR.M. WEST, ESO

On the unique occasion of the “FirstLight” of VLT Unit Telescope 1 (UT1),ESO went to great lengths to satisfy thedesire by the media and the public tolearn more about Europe’s new giant tel-escope. Already three months earlier,preparations were made to have relatedphotos, texts and videos available beforethe event and to involve the astronomi-cal communities in the member countriesin the presentation of the First Light re-sults.

Two slide sets were published on theWeb and as photographical reproduc-tions that illustrate VLT Milestones andthe Paranal Observatory as it looks now.A comprehensive series of 41 viewgraphsabout the VLT, its technology and scien-tific potential was published in April. Theyare useful for talks about the VLT andrelated subjects. All of this material isavailable on the Web at URL:

http://www.eso.org/outreach/info-events/ut1fl/

A 200-page VLT White Book was com-piled and published on the Web and inprinted form just before the First Lightevent. It gives an overview of this com-plex project and its many subsystems.

In order to receive and process the firstimages from VLT UT1 in the short timeavailable, a small group of ESO astrono-

mers got together at the ESO Headquar-ters to form the “First Light ImageProcessing Team”. As soon as the imag-es arrived from Paranal, they were flat-fielded and cosmetically cleaned by themembers of this group. In the late after-noon of May 26, it was decided which ofthese images should be included in theseries of First Light photos that was re-leased the following day. There were ninein all, including some that demonstratedthe excellent optical and mechanical per-formance of the VLT UT1, others whichwere more “glossy”, for instance a colourpicture with fine details in a beautifulsouthern planetary nebula.

Through the good offices of ESOCouncil members, VLT First Light pressconferences were organised in the eightESO member countries on May 27 andalso in Portugal and Chile on the sameday. In the early morning of May 27, themembers of the Image Processing Teamtravelled with the still hot press materialfrom Garching to these meetings. Mostof the meetings were opened by minis-ters or high-ranking officials from the Min-istries of Education or Science. Introduc-tory talks followed by the astronomermembers of the ESO Council and otherspecialists knowledgeable of the VLTproject. At the end, the “messengers”

from ESO presented the new images andgave a personal account of the hectic,but exciting work that had taken placeduring the previous days.

There is little doubt that these pressconferences were highly successful inconveying information about the VLT andits potential for astronomical research ina very positive way. In any case, literallyhundreds of newspaper articles, TV re-ports, etc. appeared in the following daysin all of these countries and elsewhere.

The introduction of the VLT to the Eu-ropean public and, not least, the futureusers of this wonderful new facility, hashad a good start.

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O B S E R V I N G W I T H T H E V L T

Science Verification of the VLT Unit Telescope 1B. LEIBUNDGUT, G. DE MARCHI and A. RENZINI, ESO

Introduction

The VLT first Unit Telescope (UT1) isnow being commissioned, and ESO iscommitted to deliver to its community afully tested and understood telescope byApril 1, 1999. To this end, brief periods ofScience Verification (SV) are nowplanned for the telescope and each of itsinstruments. SV data will become imme-diately public within the ESO communi-ty, and will offer the earliest opportunityof scientific return from the VLT and itsnewly installed instruments. Feedbackfrom early users is expected to be an in-tegral part of SV, with the understandingthat the system is subject to the best pos-sible check when one tries to squeezeas much science as possible out of it. Itis expected that this feedback will help toimprove and tune the systems beforetelescope and instruments are offered tothe community.

During SV of UT1 the various compo-nents of the operations will for the firsttime work as a single machine, thus mak-ing sure the systems work from end toend. This encompasses the technicalperformance of the telescope, the oper-ations of the data flow and a completetest of all the interfaces in the system.Science Verification should then demon-strate to the community the capabilitiesof the telescope and its instruments. Forcommunity astronomers, SV will deliverdata allowing them to assess promptlythe suitability of the VLT and its instru-ments for their own scientific pro-grammes, thus submitting the VLT to awider scrutiny.

Science Verification will consist of aset of attractive scientific observations,so as to involve in the process as manyscientists as possible. There will be norestrictions for the data distribution with-in the ESO member countries. However,observations of the Hubble Deep FieldSouth will be made immediately publicworld-wide, so as to parallel the releaseof the HST data.

The telescope SV is planned for Au-gust 17–31, which includes new moon(August 21), and will be conducted usingthe VLT Test Camera. A broad list of pos-sible SV observations was discussed bythe scientific management of ESO, andnarrowed to a set of higher-priority andsecond-priority observations. The surviv-ing list (see below) is still meant to over-subscribe the available time, thus allow-ing the final selection to be done on thespot, depending on the prevailing atmos-pheric conditions. The observations have

been chosen to represent typical imag-ing applications for an 8-m telescope.However, several technical restrictions(field of view, image scale and CCD char-acteristics) as well as astronomical con-straints (accessible sky) will apply.

This article summarises the plannedobservations and describes their techni-cal and operational implications. We startfirst with a summary of the technical as-pects of the VLT Test Camera, the instru-ment with which the telescope is beingcommissioned and which will be used forSV of UT1. Additional constraints are pre-sented in the next section followed by abrief overview of the calibrations. We endwith a description of the scientific goalsof the observations.

We invite all astronomers to visit theSV Web site (http://www.eso.org/vltsv/ )for further information. All SV observa-tion blocks will be available at this Webpage, as well as the full text of the SVPlan and of the VLT Test Camera Cali-bration Plan.

Science Verification has been plannedby a small team of astronomers at ESOacting under the overview of the VLT Pro-gramme Scientist. The team membersare Martin Cullum, Roberto Gilmozzi,Bruno Leibundgut (Team Co-ordinator),Guido de Marchi, Francesco Paresce,Benoit Pirenne, Peter Quinn and AlvioRenzini (VLT Programme Scientist).

The same group, together with the PIof each instrument, will plan the SV forthe instruments as well. Science Verifi-cation of FORS1 will take place inmid-January 1999, then followed by SVof ISAAC in mid-February, with each SVperiod consisting of seven nights. Theplans for the SV of these instruments willbe advertised in the next issues of TheMessenger and on the SV Web site.

External Constraints

Telescope commissioning will deliverthe Cassegrain focus for scientific obser-vations in the middle of August. The SVphase will take place just before the fo-cus will become available for the instal-lation of FORS1. The schedule for thedata flow commissioning foresees to pro-vide a functional system at the same timeso that SV can be done within the VLToperational paradigms. The data gener-ation from the definition of the observa-tion blocks, which are currently being pre-pared, to the archiving of the data in theVLT archive will be integral to SV.

The VLT Test Camera

The VLT Test Camera consists of afully reflective re-imaging system whichprovides a clean pupil and prevents di-rect illumination of the detector. The tele-scope plate scale (1.894″/mm – Casse-grain focus) is maintained. With 24 µmpixels this translates into 0.0455″/pixel.With a thinned, anti-reflection coatedTektronix 20482 CCD, this yields a fieldof view of 93″ on a side at the Casse-grain focus.

The VLT-TC will be equipped with afilter wheel with 7 positions. The filter sizeand optical parameters are the same asthe ones of the SUSI2 camera at the NTT,and the filters can be exchanged betweenthe two instruments. A standard Bessellfilter set (UBVRI) has been ordered forthe VLT-TC and it is foreseen to add aset of intermediate-band filters suitablefor photometric measurements of red-shifts. Narrow-band filters will be bor-rowed from the SUSI2 filter set, if re-quired. Neutral density filters for brightobjects are available as well.

TABLE 1: Expected signal for point source objects

(S/N in 1 hour integration)

magnitude filters

B V R I(seeing)a (seeing) (seeing) (seeing)

1.0 0.5 1.0 0.5 1.0 0.5 1.0 0.522 703 972 503 773 447 744 201 37023 321 506 217 375 187 341 82 15724 137 241 90 167 76 146 33 6425 56 106 36 70 31 60 13 2626 23 42 15 29 12 24 5.2 1027 9.1 18 5.8 12 4.9 9.7 2.1 4.228 3.6 7.2 2.3 4.6 1.9 3.9 l1 1.7

a Seeing in arcseconds FWHM

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The shutter of the camera will provideexposure times as short as 0.2 secondswhich, with the specified shutter timing,will provide a non-uniformity of 25% be-tween centre and edge of the field. Anillumination uniformity of better than 1%is achieved with exposures longer than5 seconds.

The expected signal for a point sourceis given in Table 1. The figures have beencalculated for an A0 spectrum assuminga dark sky (new moon), two reflections inthe telescope, three reflections in the testcamera, the Bessell (1990, PASP, 102,1181) filter transmissions, the CCD effi-ciency and noise parameters, and twocases of image quality.

The VLT-TC is equipped with a high-quality coronographic capability includingan occulting mask located at the UT fo-cal plane to block out light in the core ofa bright source and an apodising maskto suppress diffraction at the edges of theaperture and on the spiders. This capa-bility is there in order to carry out precisequantitative measurements of the scat-tering wings of the UT PSF. The positionand slope of these wings carry importantinformation on the scale and power spec-trum of the micro imperfections of theprimary mirror and on the size and distri-bution of dust on the mirrors. These wingsare the dominant contributors to the ex-tended halos or aureoles around the see-ing-dominated core of the PSF which limitthe contrast of the VLT even with perfectadaptive optics compensation. This facil-ity will be used to assess the effect of thePSF halo on the precision photometry offaint sources in the presence of brighterobjects.

Data Flow Operations

The operations during SV can be car-ried out fully employing the VLT data-flowsystem (Silva and Quinn, The Messen-ger 90, 12; Quinn, The Messenger, 84,30). This implies that, as far as possible,all observations will be done with obser-vation blocks (OB). Observation blocksfor each observation and the correspond-ing calibration OBs are prepared in ad-vance. The OB database for SV is thebasis for the mid-term and short-termschedules which will be prepared by theSV team for the period of interest andeach night according to the atmosphericconditions. OBs for all foreseeable con-ditions will have to be prepared so thatthe SV period will be ‘oversubscribed’ bythe available OBs to provide a sufficient-ly large selection pool of observations forany conditions.

The observations and the immediatequality assessment will be performed bythe SV team. This includes all calibrationsneeded for a complete reduction of thedata. Science Verification team membersin Garching will carry out the data reduc-tion using the data reduction pipeline.

Archiving of the data will be the re-sponsibility of the VLT archive and the

SV team will not assume a role here.However, reduced data (e.g. object mag-nitudes) should be made availablethrough the archive when released by theSV team in Garching.

Boundary Conditions

The sky coverage of the VLT at theend of August will be from RA of 14h to7h. The declination range reaches fromthe Southern pole all the way to +40°. Theaccessible sky at the end of August isshown in Figure 1.

For scientifically interesting observa-tions, we have to explore the unique fea-tures of the VLT-TC. As a simple imager,the VLT-TC has presumably among thehighest throughput of any (imaging) in-struments on an 8-m telescope. The re-flective optics make the UV wavelengthrange down to the atmospheric cut-offaccessible. The large oversampling ofany seeing condition will make the accu-rate determination of point spread func-tions possible, which is a pre-requisite forPSF subtraction. For most extended ob-jects and point sources which do not haveto be largely oversampled, it will be ad-vantageous to bin the CCD to reduce theeffect of readout noise, although, forbroad-band filter observations, theVLT-TC will work in the background (sky)limited regime most of the time.

Calibrations

The simplicity of the VLT Test Cameraalso means that the calibrations are re-stricted to only a few subsystems. TheCCD calibrations will include bias sub-traction and (sky and dome) flatfield divi-sion. Dark frames will be acquired tocheck for the dark current. A bad pixelmap will be constructed and may be usedfor some of the observations. Also fringeframes in the case of narrow-band imag-ing may be required. Other checks for thecamera include the CCD linearity andshutter calibrations. We do not anticipatethat corrections for these will be neces-sary, but will acquire the necessary datafor control.

Photometric calibration will beachieved through the observation ofstandard stars. Colour terms for the in-strument throughput and second-orderextinction coefficients should be estab-lished during SV. In the case of narrow-band imaging, we plan to observe spec-trophotometric standards to calibrate thefilter transmission.

The VLT Test Camera calibration plangives a detailed description of the plannedcalibration observations and also de-scribes templates and template parame-ters. The plan is available at the SV Website.

Planned Observations

In the following sections the plannedscience observations are described. They

have been sorted into two priority groups.The first set describes the higher-priorityobservations which will be attempted first.The second group of observations aremaintained as backup should the condi-tions be very favourable. We give hereonly a very brief account of these obser-vations and refer interested astronomersto the SV Plan available at the SV Website.

Criteria for the Selectionof SV Observations

The following guidelines were adopt-ed for the selection of the observations:

(1) scientific attractiveness,(2) broad range of “topics” (from So-

lar-system objects to very high-redshifttargets) to ensure involvement of a largefraction of the community,

(3) projects which are generally pho-ton starved,

(4) low-surface brightness objects,(5) observations which require a large

dynamic range,(6) faint ultra-violet objects,(7) time-resolved photometry of some

very faint objects.Even with this set of criteria a certain

degree of arbitrariness is inevitable, whenit comes to the selection of specific tar-gets. We are sure everybody will under-stand.

Though the VLT image quality is ex-pected to be outstanding among theground-based telescopes, it makes nosense to attempt using the VLT test cam-era to compete on image quality withHST.

The observations described in the fol-lowing section are targeted at represent-ative astronomical objects, but it is notplanned to observe complete samples ofobjects.

During the SV period of UT1 the Ga-lactic plane is accessible for part of thenights, but also a fair fraction of the “ex-tragalactic sky” can be observed (Fig. 1).Three of the four EIS fields and theplanned Hubble Deep Field South arealso accessible to the VLT during SV. TheSV team will run the telescope with flex-ible scheduling mixing observations ofdifferent scientific goals depending on theactual conditions.

Higher-Priority Observations

Hubble Deep Field – South

The HDF-S will be optimally observa-ble in late August, and certainly this fieldwill attract a great deal of follow-up workboth from ground and space in the nextfew years. The SV plan is to observe theSTIS field containing the quasar at red-shift 2.54 and the two NICMOS fields.Deep imaging of the NICMOS fields inUBVRI will complement the near-IR HSTdata. The quasar will be observed in anarrow-band which isolates objects emit-

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ting in Lyα at the QSO redshift to look forcompanion objects. This will also selectcandidate objects for spectroscopic red-shift observations with FORS1. Withsomewhat lower priority, one of theWFPC2 fields may also be observed withthe SUSI2 set of intermediate band fil-ters.

Detection of the Gravitational Lensresponsible for multiply-imaged QSOs

The photon collecting power of the VLTcan detect very faint surface-brightnessgalaxies. The plate scale of the test cam-era should further provide very good pointspread functions for the subtraction of thequasar images. The image quality of theVLT can be readily demonstrated withsuch observations. The luminosity pro-files of the lensing galaxies are funda-mental input parameters for the model-ling of the lenses.

In order to confirm the presence of thelens, a sequence of co-added VLT TestCamera images, together with the appli-cation of powerful deconvolution algo-rithms, should push the detection limitsto considerably fainter magnitudes. Apromising object in this category is theoptical Einstein ring.

High-z cluster candidates

Mass concentrations can be detectedby the effects they have on the light trav-el through potential wells. An easy wayto identify massive clusters of galaxiesare the distorted images of backgroundobjects (arcs). The ESO Imaging Surveywill provide a list of candidate clusters.X-ray selected candidate clusters will alsobe targeted. Detailed and systematicstudy (redshifts, structure, galaxy popu-lations, gravitational shear maps, stronglylensed background galaxies at very highredshift, etc.) will certainly form a majorset of early VLT projects. Observationsin two colours (V and I) will detect andclearly define the elliptical galaxy se-quence in the colour-magnitude diagram.The field of view of the VLT-TC is wellmatched to the expected size of high-red-shift clusters (p 30″ at z Q 1). In excel-lent seeing conditions it should be possi-ble to obtain high S/N shear maps, anddetect very high-redshift arcs, if present.

Gamma-Ray Bursters

The optical detection of Gamma-RayBursters (GRBs) has opened a new win-dow onto these enigmatic objects. Thespectral confirmation of the high-redshift

nature of some of these events has beendemonstrated. Still, not all GRBs are de-tected in the optical and their associationwith distant galaxies has not been shownin every case. Only a small number (l 5)GRBs have been actually detected in theoptical. Statistics of the gamma-ray andoptical emission will build up very slowly.Deep imaging will provide stronger limitson the optical brightness distribution ofthe host galaxies of GRBs, if present. Aproblem with the hosts of GRBs has beentheir relative faintness. The three casesinvestigated so far show sub-luminous(m L*) objects, which may rule out verymassive stars as progenitors of GRBs.Imaging of sites of optically identifiedGRBs could provide more information onthis issue. Should there be a GRB alertduring SV with an error box not exceed-ing the field of view of the VLT-TC, wewould certainly attempt an identificationand observe its afterglow.

The imaging of a former GRB site isnot a problem. Imaging of former sites ofGRBs will also prepare the spectroscop-ic observations by FORS1.

SN 1987A

The shock from the supernova is pre-dicted to reach the inner ring only in the

Figure 1: Accessible sky (white area) for SV of UT1 (end of August). The galactic plane is indicated by the thick line. The Galactic Centre(circle),the EIS fields (open squares), position of HDF-S (filled square), the LMC and SMC (hexagons), and the galaxy clusters Virgo, Fornax and Abell370 (dots) are marked.

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next decade. However, it is starting toionise material left over by the fast, hotstar wind. An HII region inside the ring,i.e. gas ionised by the progenitor Sk −69201, has been stipulated to be responsi-ble for the observed slow-down of theshock in the radio. X-ray emission is alsoassociated with the shock interaction re-gion. If there are substantial amounts ofionised gas inside the ring, it should beat very low surface brightness. It still hasnot been detected conclusively. Narrow-band imaging in Hα and [O III] is the bestchance to see this emission with the VLT.STIS has detected high-velocity Lyα frominside the ring. The ring itself has startedto brighten in a single spot. So far it isundecided whether this brightening is dueto changing ionisation or an early inter-action of material which did not suffer anybraking by shocks.

UV imaging of HST fieldsin globular clusters

One of the most intriguing, yet mostinteresting aspects of globular clusterdynamics is the fate of these systemsafter core collapse. While it is today dem-onstrated, on solid theoretical grounds,that they all must undergo this catastroph-ic phase on a timescale of order p 10Gyr, it is still not at all clear how the stel-lar population in their cores would reactto strong densities (up to p 109 M0 pc−3)such as those expected to accompanythe gravothermal instability. Coupled withthe relatively low velocity dispersion ofthe stars in the core, such an extremelyhigh density sets the ideal conditions forthe formation of hard binaries, which willeventually heat the cluster core. Closebinary systems and cataclysmic variablesare, therefore, expected to play a domi-nant role in the post-collapse evolutionof clusters, and should populate in largeamounts the densest cores which are athigher risk of collapse.

Although only a few cataclysmic bina-ry systems have so far been detected inglobular clusters from the ground, a ran-dom and sporadic search for blue varia-ble objects in globular cluster cores con-ducted with HST has already turned upquite a good number of interacting bina-ries. While no ground-based instrumentcan achieve the spatial resolution need-ed to peer deep into the cores of denseclusters, the collecting area of the VLTand the good near-UV sensitivity of theVLT-TC, coupled with the astrometric in-formation of the available HST data, canserve this job by allowing us to locate allthe variables in the cores and to obtain agood light curve of the objects having aperiod in the 2–10 hr range as might beexpected from most interacting andeclipsing systems. We will then be able

to evaluate observationally the influenceof these binaries on the dynamical evo-lution of the clusters. Images will be ana-lysed with a restoration technique whichmakes use of high-resolution astromet-ric information to reach high-quality pho-tometry of stellar objects in ground-basedcrowded fields.

Timing of Pulsars

The first pulsar detected in γ-rays,Geminga (PSR J0633+1746), is one ofthe most mysterious objects in the sky.Its parallax and proper motion have beenmeasured and its luminosity has beenobtained at various wavelengths. It car-ries all signatures of an isolated coolingneutron star. The period derivative meas-ured in the γ-rays suggests an age ofabout 3.4 × 105 years, typical of a fairlysettled object. Geminga has been ob-served as a faint optical source at B Q26.5. Recently, optical pulses have beenreported from this object. Already fivepulsars have data on optical pulses, allwith photon-counting devices. TheVLT-TC should be able to detect the op-tical pulses of some of these objects aswell. The pulse measurement can beachieved by repeated integrations whilemoving the charge on the CCD. Since thepulse period is known very accuratelyfrom observations at other wavelengths,we can move the image on the CCD atthis period and detect the pulse shapeand any thermal, inter-pulse emission.

Lower-priority observations

Giant arcs in clusters

Through the amplification of the lightby gravitational lenses, we are able toexamine faint objects at larger distancesin the Universe than allowed by othertechniques. Observations of lensed gal-axies can provide important new insightsinto their formation and chemical evolu-tion as well as clarify when in time theseprocesses took place. Broad-band obser-vations of distorted galaxies have beenused to infer the redshift distribution to R= 27. Since the asymmetry is best ob-served at the faint, outer isophotes, theVLT can significantly increase the S/N.

Quasar host and companiongalaxies

The intense radiation emitted by QSOsmust have a significant impact on theirhost galaxies. Very few host galaxies ofquasars have been observed so far be-cause of the strong contrast between theluminosity of the galaxy and that of theQSO. The morphologies of these objectsspan all known galaxy types including

disturbed systems. Since, however, nocolour information is available to date, thecurrent star-formation rate or its historyremain still unexplored. Detecting hostgalaxies of quasars and determining theiraccurate colours through broad-bandimaging can teach us about the influenceof the central power house on the sur-rounding material.

The large brightness contrast betweenthe bright nuclear region and the galaxyrequires a large photon-collecting powerand small pixel sizes so as not to satu-rate the point source, yet still reveal thecomparatively faint surface brightnesshost.

Proper motion projects:Trans-Neptunian objects

The current inventory of the outer So-lar System includes about 50 Trans-Nep-tunian objects (TNOs), whose orbitsemi-major axis is in the 30–45 AU range,7 Centaurs, orbiting between Saturn andNeptune, and many Short-Period andLong Period Comets (SP and LP respec-tively, a few hundred in total).

The dynamical studies and theoreti-cal models of these populations link theirformation to different regions of the So-lar System: while the LP comets wereformed in the Jupiter-Saturn region, thenejected by these planets to the outer So-lar System, forming the Oort Cloud(s), theSP comet would have formed in situ, to-gether with the TNOs, in 30–150 AU eclip-tic region, forming the Kuiper Belt. Thescattering of some of these comets andTNOs by the planets caused them to mi-grate on to larger orbits. The outwardmigration of Neptune caused its accom-panying orbital resonance to sweep abroad region of the inner Kuiper belt, andexplains the observed eccentricity distri-bution of the observed TNOs. The majorproblem is that these models need ob-servational support: for most of the TNOsdiscovered, the only magnitude availableis a crude estimate made from the dis-covery image, and only a few have col-our measurements. About a dozen ofshort-period comets and a couple of theCentaurs have been measured.

With projected proper motions in therange of a few arcsec per hour and mag-nitudes around V Q 23–26 for a typicalTNO, several short exposures will haveto be collected for each object in order tominimise tracking problems. Candidatesare available around the ecliptic, howev-er, there is a concentration near 0h and12h RA due to selection effects (low stardensity).

B. Leibundgutbleibund@eso.org

9

Scientific Evaluation of VLT-UT1 ProposalsOBSERVING PERIOD 63 (APRIL 1 – OCTOBER 1, 1999)

The procedure for time allocation on the VLT and on the La Silla telescopes will basically follow the same principles, i.e.• Observing proposals will have to be submitted every six months.• The scientific evaluation of the VLT proposals and the proposals for the La Silla telescopes will be performed at the sametime and by the same OPC and Panels.For Observing Period 63, the submission of proposals and the related OPC activities will follow the time table given below:

August 1, 1998 Web release of the Call for Proposals for the Paranal and La Silla observatories. This release willinclude a new application form.

October 1, 1998 Deadline for the submission of VLT-UT1 and La Silla proposals

October 15, 1998 Distribution of the VLT-UT1 and La Silla proposals to members of the OPC Panels, and to thedirectors of the Paranal and La Silla observatories for technical feasibility assessment

November 2, 1998 Distribution of the technical feasibility reports to the members of the OPC Panels

November 25, 1998 Deadline for submission of reports by the members of the OPC Panels

Nov. 30 – Dec. 4, 1998 Meetings of the Panels and of the OPC

First VLT Call for ProposalsP. QUINN, J. BREYSACHER, D. SILVA

1. Introduction

On 1 August 1998, ESO will releasethe Period 63 call for proposals for allESO telescopes. For the first time this willinclude the 8.2-m Unit Telescope 1 of theVLT. The deadline for proposals will be1 October 1998 for all telescopes whichrepresents an increase of one month inthe preparation period from previousrounds. The OPC will meet in the firstweek of December 1998 for both UT1 andLa Silla telescopes (see the box “Scien-tific Evaluation of VLT-UT1 Proposals” inthis issue). Period 63 operations will com-mence on 1 April 1999. Proposals forPeriod 64 will be called for on 1 February1999 and close 1 April 1999.

During Period 63, UT1 will offer instru-ments in both Service Mode and VisitorMode. It is ESO’s intent to ultimately of-fer Service Mode observations for allmost frequently used modes of instru-ments on the VLT in order to permit thebest utilisation of the unique propertiesof the Paranal site and to guarantee aminimum level of consistency to the ar-chived data. As we accumulate experi-ence on the most effective use of the in-struments and develop adequate soft-ware tools, we plan to support service aswell as visitor observing with automatedcalibration pipelines to initially removeinstrument signatures and ultimately toprovide physical quantities. Initially, suchpipelines will exist only for the simplestmodes of use of the instruments offered.Service observing can “of course” becarried out without the benefit of suchstandardisation in the same manner that

visitor observing is carried out. This modeof operation is much more manpower in-tensive and will be offered on a best-effort basis. ESO will work closely withthe user community to develop serviceand visitor mode operations and resourc-es that will maximise the scientific returnof the VLT.

In Service Mode, successful principalinvestigators will specify observation pro-grammes as a series of ObservationBlocks (OBs) using Phase 2 ProposalPreparation (P2PP) software tools (seeSilva and Quinn, December 1997, TheMessenger). These OBs will be execut-ed by ESO staff astronomers on UT1 toa schedule dictated by OPC ranking andprevailing conditions. In Visitor Mode,astronomers will again construct OBs butwill journey to Paranal and be presentwhen they are executed.

2. Instruments for UT1 inPeriod 63

ESO plans to offer FORS1 and ISAACon UT1 beginning in April 1999. De-tailed descriptions of these instrumentscan be accessed from the ESO Web

page http://www.eso.org/instruments.All VLT instruments are commis-

sioned in two phases. In the first phase,the instrument is mounted on the tele-scope for the first time and functionaltests are made of all operational modes.This phase is followed by an assess-ment period where instrument perform-ance is evaluated and observing tem-plates are optimised. The second andfinal commissioning phase sees opera-tional tests of all observing modes tobe offered to the community. Each in-strument then enters a Science Verifi-cation period in which test science pro-grammes are executed under actualoperations conditions to assess scienceperformance and readiness for opera-tions. At this time ESO is planning tocarry out the commissioning schedulefor FORS1 and ISAAC outlined in Ta-ble 1.

The final set of instrument modes andthe measured instrument performanceon UT1 offered to the ESO communityon 1 April 1999 will depend on the re-sults of the commissioning and scienceverification processes. Principal investi-gators may have to make modificationsto observing programmes in early March

TABLE 1: FORS1 and ISAAC Commissioning Periods.

Instrument Phase 1 Phase 2 ScienceCommissioning Commissioning Verification

FORS1 10/9/98 – 4/10/98 10/12/98 – 26/12/98 14/1/99 – 20/1/99ISAAC 14/11/98 – 4/12/98 4/2/99 – 17/2/99 18/2/99 – 24/2/99

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1999 based on the outcome of commis-sioning.

Tables 2 and 3 present the FORS1 andISAAC instrument modes ESO plans tocommission by 1 March 1999 and offerduring Period 63.

3. Application Process forPeriod 63

Observing proposals for all ESO facil-ities on La Silla and Paranal will use arevised application form. Although revi-sions were necessary to provide VLT sup-port, ESO took this opportunity to stream-line the form in many areas and to pro-

vide the capability to include Postscriptfigures.

As usual, the La Silla Call for Propos-als will only be available from the ESOWeb site.

A separate VLT Call for Proposals willbe published both on paper and on theWeb. The VLT Call for Proposals willcontain all the information necessary tocomplete and submit a VLT observingproposal, including a description of thedetailed supplementary documentationavailable to proposers. Such detaileddocumentation includes the VLT WhiteBook (a technical overview of the entireVLT facility) and the individual instrument

TABLE 2 : Modes for FORS1 in Period 63.

FORS1 Instrument Mode Pipeline in Period 63

Direct Imaging YesMultiobject Spectroscopy NoLongslit Spectroscopy YesImaging Polarimetry NoSpectropolarimetry No

TABLE 3 : Modes for ISAAC in Period 63.

ISAAC Instrument Mode Pipeline in Period 63

Short Wavelength Imaging Yes

Long Wavelength Imaging(without chopping) No

Short Wavelength Spectroscopy YesLong Wavelength Spectroscopy(without chopping) No

handbooks. The VLT Call for Proposalswill also provide the information neces-sary for proposers to decide whether Vis-itor Mode or Service Mode is more ap-propriate for their project. Informationabout the FORS1 and ISAAC ExposureTime Calculators (ETCs) and how theycan be used to support the proposal proc-ess will also be provided. Preliminaryversions of the FORS1 and ISAAC ETCsare available via the ESO Web site athttp://www.eso.org/observing/etc.

Astronomers preparing VLT observingproposals should be aware that if theyare awarded VLT time, they will be askedto complete a Phase 2 proposal process.During the Phase 2 process, proposerswill create detailed descriptions of theirobserving programme in the form of Ob-servation Blocks (OBs). Visitor Mode PIswill be strongly encouraged to constructtheir OBs before traveling to Paranal butwill not be required to finalise their OBsuntil after they have arrived there. Serv-ice Mode PIs, however, will be requiredto submit their OBs to ESO before theirprogramme will be executed. More infor-mation about this process will be provid-ed in the VLT Call for Proposals. Astron-omers planning to propose for VLT timemay also wish to read Silva & Quinn (TheMessenger, December 1997) and Silva(this issue). A detailed guide to prepar-ing OBs using Phase 2 tools will be pub-lished in the December 1998 Messenger.

Astronomers with further questionsregarding the call for proposals for Peri-od 63 are asked to contact the User Sup-port Group at ESO (usg@eso.org).

P. Quinnpquinn@eso.org

In this evening view, obtained about half an hour after sunset, the UT1 telescope structure is seen through the dome slit. The assembly of UT2 iswell on its way in the next dome, and the first parts of UT3 are in place in the third.

11

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

AMBER, the Near-Infrared /Red VLTI Focal InstrumentR.G. PETROV 1, F. MALBET 2, A. RICHICHI 3, K.-H. HOFMANN 4

1Université de Nice – Sophia Antipolis, and Département Fresnel, Observatoire de la Côte d’Azur, France (OCA)2Laboratoire d’Astrophysique, Observatoire de Grenoble, France (LAOG)3Osservatorio Astrofisico di Arcetri, Italy (OAA)4Max-Planck-Institut für Radioastronomie, Germany (MPlfR)

Abstract

The near-infrared / red focal instrumentof the VLTI, called AMBER, will operatebetween 1 and 2.5 µm in a first phase(2001–2003) with two UTs. This instru-ment has been designed for three beamsto be able to perform images throughphase closure techniques. The wave-length coverage will be extended in asecond phase down to 0.6 µm at the timethe ATs become operational. The magni-tude limit of AMBER is expected to reachK = 20 when a bright reference star isavailable and K = 14 otherwise. The mainscientific objectives are the investigationat very high angular resolution of disksand jets around young stellar objects andAGN dust tori with a spectral resolutionup to 10,000.

1. Introduction

The interferometric mode of the VLT(VLTI) has always been present in the VLTproject. In the last Messenger issue (No.91, March 1998), the ESO Director Gen-eral, Riccardo Giacconi, has presentedthe role of ESO in European Astronomyby stressing the important and unique sci-entific contribution expected from theVLTI. The VLTI implementation plan hasbeen reviewed in 1995–1996 by ISAC,the Interferometry Science Advisory Com-mittee, who gave its recommendation tothe ESO community in The MessengerNo. 83 (March 1996). The committee rec-ommended early operations of the VLTIas well as a phased development thatwould focus in the infrared wavelengthrange (1–20 µm). A new plan has thenbeen proposed by the ESO VLTI teamwith an updated timetable: operations withtwo 8-m unit telescopes (UTs) before the

end of 2000, with two 1.8-m auxiliary tel-escopes (ATs) before the end of 2002 andthe full complement of 4 UTs and 3 ATsstarting in 2003. In 1997, three instru-ments were proposed:

• AMBER, Astronomical Multi BEamcombineR: a near infrared / red instrument(0.6–2.5 µm). At this time, AMBER includ-ed adaptive optics.

• MIDI, MID-infrared Interferometricinstrument: a thermal infrared instrument(10–20 µm).

• PRIMA, Phase Referencing Imagingand Micro-arcsecond Astrometry: an in-strument based on the simultaneous op-eration of two fields.

On 14 April 1998, the VLTI SteeringCommittee recommended that ESO takethe lead to deliver a dual field and stabi-lised beams (adaptive optics and fringetracking), in order to boost the perform-ance of AMBER and MIDI, as early as in2001, much earlier than expected in thefirst version of the instrumentation plan.

AMBER intends to combine the mainadvantages of the interferometric instru-ments for which Europe has acquiredexperience: the FLUOR instrument [1, 2]and the GIST interferometer [6].

This paper presents a preliminary re-port on AMBER, where we detail the sci-ence drivers, the concept, the expectedperformance and the overall project or-ganisation. The work presented here isthe result of two preliminary workinggroups [4, 5] in addition to the AMBERpresent group [7].

2. Science Objectives

Of course, a major role in the scienceoperation of AMBER will be played by thelimiting magnitude that the system willpermit (see Section 4). With such sensi-

tivities, there is a wealth of scientific is-sues that AMBER will allow us to tackle.Within the project, it has been decidedthat, at least at an initial phase, the in-strument should be dedicated to relativelyfew topics. An investigation based on cri-teria of feasibility on one side, and stronginterest in the scientific community on theother side, has resulted in a few selectedareas which are listed, with a list of typi-cal parameters, in Table 1.

It is important to note that AMBER willallow us in principle to cover a wide rangeof scientific objectives including:

• the search of hot exoplanets• the formation and evolution of stars• extragalactic studieswhich will be our first scientific targets.

A detailed description of the scientific ra-tionale cannot be given in full here, butthe reader is referred for instance to theproceedings of the workshops organisedby ESO (Science with the VLT, Walsh andDanziger eds.; and Science with the VLTInterferometer, Paresce ed.).

3. Preliminary Optical Layout

Figure 1 shows a possible optical lay-out of AMBER which is mainly intendedto illustrate the functions of the differentmodules of the instrument. Three partsmust be distinguished. Firstly, each beamis processed independently (1–4 in thefigure); then they are combined (5–8);and finally a spectrograph and a detec-tor (9–13) analyse the combination focus.The figure represents a layout for threetelescopes.

The incoming beams have their wave-fronts corrected by low-mode adaptiveoptics modules provided by ESO for theUTs and by the AMBER consortium forvisible wavelengths. The expected Strehl

TABLE 1: Scientific characteristics for AMBER

Target Visibility Minimum Wavelength Spectral Polarisation 3 beams Wide-fieldAccuracy K magnitude coverage resolution useful useful useful

Exozodi / Hot exoplanets 10–4 5 K 50 N N Y / NStar-forming regions 10–2 7 JHK+lines 1000 Y Y YAGN dust tori 10–2 11 K 50 Y Y YCircumstellar matter 10–2 4 JHK+lines 1000 Y Y YBinaries 10–2 4 K 50 N N YStellar structure 10–4 1 lines 10000 N Y N

12

ratio should reach 0.5 for the Unit Tele-scopes in the K band and should remainas high as 0.25 for reference stars ofmagnitude V P 15. The optical path dif-ferences between the beams are com-pensated by an ESO fringe tracker.Thanks to the dual field, wavefront cor-rection and fringe stabilisation can beperformed on a star up to 25 arcsecondsaway from the scientific target.

The compressed pupil after the cylin-drical optics has the same shape what-ever the number of telescopes. We planto use the same spectrograph and de-tector in all cases. Therefore, increasingthe number of telescopes from two tothree, and then to four, requires only theaddition of one incoming beam with thecorresponding optics and the modifica-tion of the anamorphic system withoutchanging anything in the already existingbeams.

The effect of the spatial filter is to re-duce the wavefront perturbations to a fluxvariation in the fibre [3]. If these photo-metric fluctuations are measured with agood precision, and if the fringe exposuretimes are short enough, then the fringevisibility can be measured with no exper-imental bias as has been demonstratedby the FLUOR experiment. The spatialfilter and the photometric calibration aretherefore necessary to measure visibili-

ties with extremely high accuracy (our am-bitious target is 10–4) on relatively brightsources (up to K P 9). With the spatial fil-ter, the instrument has a field limited bythe size of the Airy disk of the individualtelescopes.

4. Expected Performances

At this stage of the project, this param-eter is still subject to several uncertain-

Figure 1: Preliminary optical layout of AMBER.An afocal system (1) is used to compress the incoming

beams. Babinet-like prisms (2) intend to correctthe difference in polarisation which might be introduced in

the different beams by non homogeneities of the coatings. A second set ofprisms (3) may correct chromatic effects such as the atmospheric dispersion and/or

differential refraction. The key feature (4) of the AMBER instrument is an off-axisparabola that feeds a short optical fibre acting as a spatial filter and isolating a single

coherent mode. Second off-axis parabolas produce parallel beams which are reflected onbeamsplitters (5), the first part of the beam combiner. The two closest beams are almost tangent

and the third one is two beam diameters away (centre to centre) from the second one. These beams producesuperimposed Airy disks and each pair of pupils will produce a set of fringes. Due to the non redundant spacing of the pupils,

this set of fringes can be discriminated by their spatial frequency. An anamorphic system (7) made of a pair of cylindricalmirrors in an afocal combination compresses the beam orthogonally to the fringes. The flat mirrors (6, 8) reflect the photometric

beams used for calibration of atmospheric fluctuations. Cold stops on a wheel (9) and a filterwheel (10) are located at a pupil position. The light is then dispersed by a grating (11). Acompact spectrograph design requires two chamber mirrors (12). The detector (13) will prob-ably be 1024 × 1024 HAWAII Rockwell array. With three telescopes, the fringes are analysedwithin a strip of 12 × n pixels, where n is the number of spectral channels (n L 1024). Thephotometric beams are slightly dispersed by a fixed prism (14) to take into account the chro-matic variations of the Strehl ratio and the spatial filter efficiency. For some objects, we planto use the 2″ non-vignetted field available in the VLTI laboratory. This is achieved by replac-ing the spatial filter unit by an afocal system without spatial filter (4a′, 4c′) which maintains thedirection of the output beam but divides its diameter by two. The figure roughly respects theproportion between the elements. The size of the spectrograph is 45 cm × 30 cm.

13

ties linked to exact specifications of op-tics throughput, detector and electronicscharacteristics, as well as fringe trackerand adaptive optics performance. Atpresent (see Table 2), we estimate thatAMBER coupled to the VLT UT tele-scopes should allow us to reach, when abright star reference is available, K lp 20in broad band and K lp 15 at a resolutionof 1000. When the interferometer usesthe object as a reference, the limitingmagnitude is rather K lp 14. At the 1.8-mAT telescopes these limits drop by about2.7 mag.

The upper half of Table 2 gives the lim-iting magnitudes of AMBER when the in-strument detects fringes on the scientificsource (self-reference mode). Thesenumbers would also be the limits for thefringe sensor (for example the ESO/OCAPrototype Fringe Sensor Unit equippedwith PICNIC detector with 18 electronsread out noise, Rabbia et al., 1996). Inthis mode, AMBER can detect fringeswith λ/4 accuracy on stars up to K = 14with 25-ms exposure time. For starsbrighter than K = 9.7, the fringes can bedetected at λ/40 accuracy with 4-ms ex-posure time. In this self-referencingmode, the limiting magnitudes are validfor all spectral resolutions.

The dual field allows for off-axis refer-ence stars. The limiting magnitude forthese references are the same as theones quoted above. The lower half of Ta-ble 2 gives the limiting magnitudes on thescience object in order to reach a 1% vis-ibility accuracy within 4 hours of obser-vation sliced into 100-second individualexposures.

These numbers are given for poorlyresolved objects producing maximumfringe contrast in the fringe sensing spec-tral band. A 0.1 object visibility would leadto a 2.5 mag penalty.

5. Organisation

5.1 Institutes involved

The AMBER consortium is composedof four institutes:

• Laboratoire d’Astrophysique, Ob-servatoire de Grenoble (LAOG, France).

• Observatoire de la Côte d’Azur(OCA, France)

• Osservatorio Astrofisico di Arcetri inFirenze (OAA, Italy)

• Max-Planck-Institut für Radioastron-omie in Bonn (MPlfR, Germany).

Other institutes provide expert scien-

tists or engineers but do not build or inte-grate hardware. They are:

• Institut de Recherche en Communi-cations Optiques et Microondes in Limo-ges (IRCOM, France)

• Université de Nice – Sophia Antipo-lis (France)

• Office National d’Études et de Re-cherches Aerospatiales in Paris (ONERA,France),

• Centre de Recherche Astronomiquede Lyon (CRAL, France).

5.2 Project structure

The AMBER project includes a princi-pal investigator (PI: R. Petrov OCA), aproject scientist (PS: F. Malbet LAOG), achairman of the science group (SGC: A.Richichi OAA), a project manager (PM:P. Kern LAOG), a system engineer (SE:S. Ménardi OCA) and a co-investigator(CoI: K.-H. Hofmann MPIfR). AMBER hasbeen divided in a set of working groups,each one in charge of one AMBER sub-system.

In addition to the ESO ISAC (Interfer-ometry Science Advisory Committee),there is a science group for each VLTIinstrument with the task of identifying andprioritising the key targets in order to max-imise the scientific return of the instru-ment, especially during early operations.In the case of AMBER, the science group(SGR) includes scientists working on starformation, galaxies, AGN, exoplanets,low-mass stars, AGB stars, Be stars andcircumstellar medium. The project scien-tist (PS) is in charge of translating the sci-entific needs in terms of instrument spec-ifications. He is helped by an interferom-etry group (IGR), for interferometry offersa large range of observing modes andprocedures, whose priorities must be an-alysed and specified by specialists.

The subsystem working groups of theAMBER instrument are:

• Optomechanics• Cooled spectrograph• Detector and associated electronics• Instrument control (VLTI interface

included)• Observations support (observation

preparation, data reduction)• Testing, integrating equipment and

performance tests.

5.3 Budget

Many elements still have to be de-fined in the present system definition

phase. Therefore, the final budget can-not be completely defined before thePreliminary Design Review (PDR) in No-vember 1998. The estimated final budgetfor the hardware of the infrared part ofAMBER for two beams (phase 1) is 4MF ±10%. Extension to three beams andto visible wavelengths (phase 2) requireadditionally 4 MF ±30% including theadaptive optics modules for two ATs (1MF each).

The preliminary and still approximategeneral timetable combines the planningfor each subsystem and integrates themin a general planning with the followingimportant dates:

• July 1998: Full definition of the project(Final Concept Review). Problems havebeen identified and a concept has beenselected.

• November 1998: Preliminary DesignReview. Problems have been solved,detailed system analysis is finished. Allinterfaces are analysed. Precise time-table is known.

• April 1999: Final Design Review. Allorders can be issued.

• July 2000: Manufacturing and Inte-gration Review. All subsystems have beenintegrated and tested and it is possible tostart the global integration and tests.

• December 2000: Shipment toParanal where, after 3 months of labora-tory and siderostat tests on site, we ex-pect to start observations.

• April 2001: Observations with theUTs.

Note:

The AMBER documentation is avail-able on the following Web site:

http: //www-laog. obs.ujf-grenoble.fr/amber

References

[1] Coudé du Foresto V., Ridgway S. 1991,FLUOR: a Stellar Interferometer UsingSingle-Mode Infrared Fibers. In: Beckers J.,Merkle F. (eds.) Proc. ESO Conf., High-resolution imaging by interferometry II.ESO, Garching, 731.

[2] Coudé du Foresto V., Perrin G., MariottiJ.-M., Lacasse M., Traub W. 1996, TheFLUOR/IOTA Fiber Stellar Interferometer.In: Kern P., Malbet F. (eds) Proc.AstroFib’96, Integrated Optics for Astro-nomical Interferometry. Bastianelli-Guiri-mand, Grenoble, p. 115.

[3] Coudé du Foresto V. 1996, Fringe Benefits:the Spatial Filtering Advantages of Single-

Two UTs

Fringe accuracy λ/4 λ/40Self-reference 14 9.7

Spectral resolution Broad-band 100 1000 10000Off-axis reference 20.7 17.7 15.2 12.7

Two ATs

Fringe accuracy λ/4 λ/40Self-reference 11.3 7

Spectral resolution Broad-band 100 1000 10000Off-axis reference 18 15 12.5 10

TABLE 2: Expected limiting magnitude for two UTs (left) and two ATs (right). See text for details.

14

Mode Fibers. In: Kern P., Malbet F. (eds)Proc. AstroFib’96, Integrated Optics forAstronomical Interferometry. Bastianelli-Guirimand, Grenoble, p. 27.

[4] Malbet F., Coudé du Foresto V., MékarniaD., Petrov R., Reynaud F., Tallon M. 1997a,Étude préliminaire de l’instrument proche-infrarouge / rouge du VLTI et de GI2T,available on the AMBER Web (AMB-REP-001).

[5] Malbet F., Perrin G., Petrov R., Richichi A.,Schöller M. 1997b, AMBER Report 2 – The

imaging and spectroscopic VLTl focal instru-ment, available on the AMBER Web(AMB-REP-002).

[6] Mourard D., Tallon-Bosc I., Blazit A.,Bonneau D., Merlin G., Morand F., VakiliF., Labeyrie A. 1994, A&AS 283, 705.

[7] Petrov R., Malbet F., Antonelli P., FeautrierPh., Gennari S., Kern P., Lisi F., Monin J.-L.,Mouillet D., Puget P., Richichi A., RoussetG. 1998, AMBER, The near infrared / redVLTI focal instrument, Report for the Steer-ing Committee meeting, 30 January 1998.

Available on the AMBER Web (AMB-REP-003).

[8] Rabbia Y., Ménardi S., Reynaud F., DelageL. 1996, The ESO-VLTI Fringe Sensor. In:Kern P., Malbet F. (eds) Proc. AstroFib’96,Integrated Optics for Astronomical Interfer-ometry. Bastianelli-Guirimand, Grenoble, p.175.

F. MalbetFabien.Malbet@obs.ujf-grenoble.fr

NEWS FROM THE NTTG. MATHYS, ESO

The NTT Upgrade Project has cometo an end at the end of March. Over thepast 4 years, the readers of this columnhave been able to follow the progress ofthis project through its three distinctphases: the stabilisation of the opera-tions of the NTT, the installation at theNTT of the VLT control system, and theuse of this refurbished facility for scien-tific observations within the frameworkof the VLT operational model (see TheMessenger Nos. 75 to 91). The upgradeproject has fulfilled its objectives ofstrengthening the NTT as a world lead-ing 4-metre-class telescope and of us-ing it as a testbench for the technicaland operational concepts and solutionsadopted for the VLT, prior to the entry ofits first unit telescope into operations.With consideration for the latter objec-tive, the NTT Upgrade Project has beenconducted under the overall responsi-bility of the ESO VLT Division (but withimportant resources of other divisions,in particular the La Silla Division). Nowthat the project is completed, quite nat-urally, NTT operation has come backsince the beginning of Period 61 underthe responsibility of the La Silla Divi-sion, like all the other ESO telescopeson La Silla.

The end of the NTT Upgrade Projectalso marks the end of the present se-ries of dedicated articles presenting“News from the NTT”, or more specifi-cally, news from the upgrade project:this note is the last one of this series.From the next issue of The Messengeron, in line with the above-mentionedreassignment of the responsibilities, in-formation about the NTT will be reinte-grated in “The La Silla News Page”. Theauthor of these lines will, as a matter offact, have left the NTT to move to theParanal Observatory and to participatein the preparation of the operations ofUT1. He will be replaced, in his functionof NTT Team Leader, by Olivier Hainaut,

who has recently joined the NTT Team(see below).

The end of the Upgrade Project

The NTT News published in the lastissue of The Messenger had been writ-ten between the installation and the com-missioning of SUSI2. The latter wascompleted at the end of February, inspite of adverse weather conditions, anda brief report was given in a dedicatedarticle by S. D’Odorico in the previousissue of The Messenger.

Bad weather also severely hamperedthe SOFI commissioning period, inMarch. In spite of the limited amount ofastronomical observations that could becarried out during the latter, its outcomewas very positive, with the successfulimplementation of a number of new fea-tures:

– an ATM connection between theLocal Control Unit (LCU) of the detectorand the instrument control and acquisi-tion workstation (wsofi). The use of sucha connection in a real-time operationalenvironment is a première at ESO. Untilnow, at the NTT as well as at the othertelescopes on La Silla, data read outfrom the detectors were transferred tothe acquisition computers through anEthernet link. For its installation at theNTT in December, SOFI also was ini-tially configured in this way. However,with the most recent increases of instru-ment performance in terms of detectorarray size and readout speed, Ethernetbecomes a bottleneck for the achieva-ble rate of data acquisition (both for theIR and for the visible: SUSI2 also suf-fers from this). In order to overcome thislimitation, the option retained by ESOfor new instruments (and existing instru-ment upgrades) is the replacement ofEthernet by ATM. SOFI is the first in-strument to benefit from this new tech-

nology. The success of its implementa-tion is a major step for the future of theESO observatories, as it paves the wayfor other instruments on La Silla (in par-ticular, the Wide Field Imager andSUSI2) and on Paranal.

– a new version of the Phase 2 Pro-posal Preparation (P2PP) tool, whichsupports the preparation of ObservationBlocks for SOFI (in addition to EMMIand SUSI2, which were already support-ed before).

– an on-line reduction pipeline for im-aging, through which, in particular, largesets of dithered images can be auto-matically combined in a very effectivemanner, taking away a large fraction ofthe burden typically affecting IR observ-ers. SOFI is the first instrument to comeon line which has been designed fromthe start for use within an end-to-enddata flow context: thanks to this, it hasbeen possible to develop for it powerfuland effective automatic reduction toolswhich are far superior to those that couldup to now be offered for conceptuallyolder-fashioned instruments such asEMMI.

On the other hand, the end of theUpgrade Project has also marked theend (or, at least, the temporary suspen-sion) of the Service Observing experi-ment at the NTT. The outcome of thelatter and the lessons that can be drawnfrom it are reported in a separate dedi-cated article in this issue of The Mes-senger. Here, it should just be pointedout that, in spite of a number of short-comings and weaknesses in what wasprimarily a learning period for both ESOand the astronomical community, Serv-ice Observing at the NTT has been quitefavourably perceived by ESO users, tothe extent that ESO has been urged byvarious of its advisory committees toconsider the possibility to keep offeringthis option at the NTT (and possibly todevelop it at other La Silla telescopes)

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in the future. The requirements and im-plications of this service are currentlybeing studied by ESO.

Current NTT Status

In the last issue of The Messenger, Ireported the emergence of a few newtechnical problems as a result of theinstallation in January of the latest ver-sion of the NTT common software atthe NTT. The two new problems withthe highest rate of occurrence in theweeks following the software upgrade,and with the most damageable impacton operations (or, in other words, thoseresponsible for the largest amount oftechnical downtime), were the sponta-neous reboots of LCUs and the randomfailures of technical CCDs. The origin ofboth was found to be related to inaccu-racies in the time distribution protocol.While the technical CCD control soft-ware was successfully modified to han-dle properly such inaccuracies and avoidfurther failures, the exact mechanism bywhich the time inaccuracies trigger theLCU reboots has not been identified yet.As a provisional workaround, LCUs arenow running on their internal clock rath-er than on a centrally distributed time.Although the internal LCU time is con-siderably less accurate, so that the cur-rently adopted option is not conceptual-ly satisfactory, it does not have any sig-nificant negative impact on the opera-tion of the telescope and of the instru-ments, and it effectively solves the an-noying problem of the LCU self-reboots.Therefore, it is quite acceptable until a“cleaner”, more permanent solution hasbeen worked out and is implemented.With it, and with the above-mentionedmodified technical CCD software, the re-

liability of the NTT control system hasnow come back to the excellent levelachieved in the last months of 1997.

From the point of view of the visitingastronomers, the end of the NTT Up-grade Project and the return of the tele-scope fully within the La Silla operation-al context should, in practice, be a verysmooth transition, since classical observ-ing at the NTT will continue to follow thescheme set up during the last year. Af-ter the completion of the major techni-cal works of the December 1997 –March 1998 period, time and resourceshave been, and will in coming monthsbe, available to refine and to consoli-date a stable operational model, in whichemphasis will be laid especially on animproved service to observers. In par-ticular, we hope to be able to provideNTT users with a few new auxiliary tools,which should allow them to have a bet-ter interaction with the system and withtheir data. One such product that hasbeen put into service on the astrono-mer’s workstation is the File HandlingTool, which provides the observer witha number of features allowing him, forinstance, to examine the headers of hisFITS files, to have a quick look at hisdata, or to take advantage of variousoptions for easy saving of his data totape.

Staff Movements

End of March, Domingo Gojak, anelectronic engineer who was in the NTTTeam since the beginning of the Up-grade Project, was transferred to theteam in charge of the 3.6-m telescopeto support the upgrade of the latter.Domingo had been one of the key play-ers in the success of the technical up-

grade of the NTT, and he will undoubt-edly play an equally important role inthe upgrade of the other La Silla majortelescope. I have enjoyed to work in thesame team as Domingo during morethan 4 years and I wish him all the bestin his new assignment.

At about the same time, Olivier Hai-naut, a former fellow from the Medium-size Telescope Team, passed to theNTT Team as a new senior staff as-tronomer. Olivier, a very experiencedobserver specialised in the study ofsmall bodies of the solar system, hasbeen designated as the future Leaderof the NTT Team, a responsibility thathe will take over from the author ofthese lines in July, after a period of over-lap which will allow him to integrate him-self in the team and to become familiarwith his future task.

Two new fellows have also joined theNTT Team, at the end of April and thebeginning of May: Vanessa Doublier, aformer student at ESO in Garching, andLeonardo Vanzi, who comes from Arcetri(Italy). Both have experience in IR ob-servations, and they will accordingly, atleast in part, be assigned to the supportof SOFI.

It is a pleasure to welcome thesenewcomers, with whom I am looking for-ward to collaborating in the last monthsof my involvement with the NTT and towhom I shall be pleased to hand overthe responsibility of this telescope, trust-ing that they will maintain it as a worldleading 4-metre-class telescope for thegreatest benefit of the ESO astronomi-cal community.

G. Mathysgmathys@eso.org

Tuning of the NTT AlignmentPh. GITTON and L. NOETHE, ESO

1. Introduction

Since the end of the NTT upgradeproject it has been known that the align-ment of the secondary mirror (M2) wasonly marginally within specification.When the atmospheric seeing was great-er than one arcsecond, the misalignmenthad no noticeable effect on the imagequality. But, under better seeing condi-tions, it was a limiting factor for the im-age quality. Therefore, it was decided totune the position of the M2 unit. We usedthe NTT wave front sensors, which arepart of the Active Optics system, in anovel way to measure the required rea-lignment of M2.

2. Effects of a Telescope Misalign-ment on the Image Quality

2.1 The NTT optics

The NTT is an aplanatic telescope ofthe Ritchey-Chretien type. Aplanaticmeans that the telescope, if it is properlytuned and aligned, is free of sphericalaberration and coma in the field. A prop-er alignment requires that the distancebetween the primary mirror and the sec-ondary mirror is correct and that the opti-cal axes of the two mirrors coincide. Theby far most important aberration remain-ing in the field is then astigmatism, whichis zero at the centre of the field and in-

creases quadratically with the field an-gle. The aberration is therefore rotation-ally symmetric with respect to the centreof the field.

In reality, any telescope is to some ex-tent misaligned. Such a misalignment willintroduce additional optical aberrations,first of all the so-called decentring coma.At the NTT, a wave-front sensor is usedto measure the aberrations affecting thetelescope. The detected coma is correct-ed by tilting M2 around its centre of cur-vature.

Since coma is not field dependent, thetelescope will then, despite the misalign-ment, be free of coma over the wholefield. But this coma correction is not suf-ficient for a complete alignment, since theaxes of the two mirrors are not yet neces-sarily coincident. In this optical configu-ration, the axes of M1 and M2 will actual-ly intersect at the coma-free point (CFP),forming an angle α (Fig. 1). The name

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CFP stems from the fact that a rotationof M2 around this point will not changethe coma of the telescope. In the NTT,the coma-free point is 1676 mm abovethe vertex of M2 (which has a radius ofcurvature of 4417 mm).

The residual misalignment of the twoaxes will destroy the rotational symme-try of the field astigmatism. This can ap-proximately be described as a shift of therotationally symmetric pattern of astigma-tism away from the centre of the field. Themeasured astigmatism may then besmaller than in the aligned configurationat some position at the edge of the field,but it will be significantly larger at theopposite side. This will lead, at least insome areas of the field and under goodseeing conditions, to a noticeable imagedegradation compared with the alignedconfiguration.

2.2 Image quality problemsreported at the NTT

Strong asymmetric variations of theimage quality under very good seeingconditions were reported for the detectorin the red arm of the EMMI instrumentwhere the diameter of the field of view isclose to 10 arcmin. The pattern of imagedegradation was actually fixed with re-spect to the telescope (and thereforeapparently rotated on the scientific de-

tector as the instruments were mountedat the Nasmyth foci).The problem wastherefore due to the telescope optics andnot to the instrument itself. Any dynamiccause (telescope tracking, vibration, ...)could also be ruled out as the effect onthe images was not uniform across thefield. This led us to question again thealignment of the M2 mirror. Indeed it hadbeen reported during the Big Bang thatthe alignment of this element was onlymarginally within specification (see“News from the NTT” by J. Spyromilio inThe Messenger No. 87). Most convinc-ing was the fact that such a misalignmentwould introduce similar effects as theones measured with EMMI.

2.3 Consequencesfor the image quality

2.3.1 PSF across the chip

As mentioned earlier, the PSF is quiteinhomogeneous across the field whichmakes any attempt of deconvolution verydifficult. This was clearly a strong limita-tion for astronomers looking for high res-olution.

2.3.2 High PSF sensitivity to focus errors

Even in the presence of astigmatism,the images are round when the telescope

astigmatism the image elongations will bestronger than in an aligned telescope.

2.3.3 Focus variation measured by thewave-front sensor

The NTT wave-front sensor measuressix modes of aberrations (defocus, de-centring coma, spherical aberration,astigmatism, triangular coma and quad-ratic astigmatism). The measurement ofdefocus is also affected by the misalign-ment of M2. Indeed the field curvature iscorrected under the assumption that theincoming optical beam is centred on theaxis of the adapter. This is not true in thecase of a misaligned M2 and, therefore,the amount of defocus was not correctlycalculated. Therefore, a specific focus se-quence had to be executed (either a thor-ough focus sequence or the use of thefocus wedge).

2.3.4 Inaccurate calculation of the on-axisastigmatism

In order not to interfere with the ob-servations, the measurements performedby the wave-front sensor are normallydone off axis although the astigmatismto be corrected is the one affecting thecentre of the field. To get the correspond-ing value of astigmatism at the centre,one has to subtract the field contributionfrom the value measured off axis. A modelassuming a rotationally symmetric fieldastigmatism therefore gave inaccurateresults for the on-axis astigmatism.

2.3.5 Out of specification condition for thefield lens

The field lens is located between thef/5.3 EMMI red camera and the CCDdetector. Its purpose is to compensatethe field curvature such that the focalplane is flat over the whole field at thelevel of the detector. With a misaligned

Figure 1: Telescope configuration after removal of coma. Figure 2: Measurement points for astigmatism mapping.

is at best focus.However, evenwith a smallamount of defo-cus, image elonga-tions will appear.For a given defo-cus, the ellipticitywill grow with theamount of astig-matism. Thismeans that at theside of the fieldwith the large

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M2 the field lens did not give the desiredresult.

3. Wave-Front Sensor as an Align-ment Tool

A method presented by B. McLeod[1] uses the measured field astigmatismto calculate the angle by which M2 hasto be rotated around the CFP. The origi-nal method deduces first the field astig-matism and then the telescope misalign-ment from the ellipticities and elongationangles of images in the field. In the caseof the NTT, this can be greatly simplifiedby using directly the output data of thewave-front sensor.

3.1 Theoretical basis

In his article, B. McLeod gives an ex-pression relating the astigmatism com-ponents (Z4,Z5) to the field angle (θx,θy)for a secondary mirror tilted by an angle(αx, αy) around the CFP.

Z4 = Ax + B0(θ2x − θ2

y) + B1(θxαx − θyαy) + B2(α2

x − α2y) (1)

Z5 = Ay + 2B0θxθy + B1(θxαy + θyαx) + 2B2(αxαy) (2)

The (Ax,Ay) terms correspond to theresidual astigmatism introduced by theM1 support on the primary mirror. Thecoefficients B0, B1 and B2 are constantsdepending on the geometry of the tele-scope. Using the optical parameters ofthe NTT we get:

B0 = − 24.3679 µm/degree2

B1 = 30.0719 µm/degree2

B2 = 0.1768 µm/degree2

3.2 The measurement procedure

In our case, the wave-front sensorallows a direct measurement of the astig-matism vector (Z4,Z5) at any position inthe field just by moving the guide probe.As shown by formulae (1) and (2), thedifference between an aligned and mis-aligned telescope is larger at the edge ofthe field due to the linear terms in θx andθy. In these equations, there are only 4unknowns (αx,αy,Ax,Ay). Theoretically,two astigmatism measurements shouldbe sufficient to deduce the misalignmentparameters. Nevertheless, we preferredto perform 9 measurements distributedover the field as shown in Figure 2.

The results of the field astigmatismmapping have then been fitted using aleast squares algorithm. The computa-tion is done completely automaticallyusing as input the log file produced bythe Active Optics system. Here are thesteps performed successively by the pro-gramme:

• retrieve guide probe positions andastigmatism measurements (Z4,Z5) fromAO log file

• convert guide probe positions to fieldoffsets (θx,θy) in telescope reference frame

• Compute M2 misalignment (αx,αy)via a least squares fit.

3.3 Misalignment data

The mapping of the astigmatism wasdone at both foci. The results are pre-sented in Table 1. σfit is the residualr.m.s. after the least squares fit. There isa reasonable agreement between thetwo foci. The averaged misalignmentangle is 0.090 degrees. Using equation(1), one can calculate the resulting high-est value cast of the coefficient of astig-matism and the corresponding diameterd80 containing 80% of the geometricalenergy both at the edge of the detectorin the EMMI red arm and at the edge ofthe field of the NTT (15 arcmin). Thevalue of d80 can directly be comparedwith the FWHM values for the atmos-pheric seeing. The values for cast andd80 are shown and compared with thecorresponding values for a perfectlyaligned telescope in Table 2.

3.4 Method for the correction of themisalignment

The active optics system allows to cor-rect the astigmatism affecting the te-lescope by deforming the primary mirror.Such a correction of astigmatism is uni-form over the whole field while the devia-tion of the astigmatism from an aligned

telescope is field dependent. The NTTactive optics system is therefore not ca-pable of restoring the optimum rotation-ally symmetric pattern of the field astig-matism.

Therefore, the only possibility to cor-rect the effects of the misalignment wasa realignment of M2, that is a rotationaround the CFP. At the NTT, the computer-controlled lateral motions of the second-ary mirror are limited to rotations aroundthe centre of curvature of M2. Therefore,the rotation around the coma free pointhad to be achieved by a combined rota-tion around the centre of curvature and atilt of M2 around its pole. The second ac-tion could most easily be performed by arotation of the whole support structure ofM2, that is by moving the spiders at theconnection points to the top ring.

4. Realignment and Results

The realignment has been performedin February just before the installation ofSUSI2 with the help of Francis Franzaand Stephane Guisard. Two opposite spi-der arms were moved in opposite direc-tion at the top ring by 1.3 mm.

New astigmatism mappings havebeen performed just after the realign-ment. They gave very good results asshown in Table 3. Overall, the misalign-ment of the M2 is now 0.018 deg whichis 5 times smaller than the previous val-ue. Table 4 shows for this new configu-ration the astigmatism values at the edge

TABLE 3: Final alignment parameters

Nasmyth focus date (σfit (nm) αx (deg) αy(deg)

A 12/02/98 157 0.002 0.016B 12/02/98 77 −0.003 0.021

TABLE 4: Final astigmatism parameters

EMMI EMMI NTT NTTCase considered cast d80 cast d80

Perfectly aligned M2 286 nm 0.121″ 1520 nm 0.641″Realigned M2 350 nm 0.148″ 1666 nm 0.702″

TABLE 1: Initial misalignment parameters

Nasmyth focus date σfit(nm) αx (deg) αy (deg)

A 18/01/98 366 0.052 0.074B 18/01/98 173 0.089 0.087

TABLE 2: Initial astigmatism parameters

EMMI EMMI NTT NTT

Case considered cast d80 cast d80

Perfectly aligned M2 286 nm 0.121″ 1520 nm 0.641″Misaligned M2 632 nm 0.266″ 2230 nm 0.940″

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of the detector in the EMMI red arm andat the edge of the field of the NTT. Thesmall differences both in the coefficientsand the d80 values at the edge of theEMMI detector between the correctedand a perfectly aligned NTT will be virtu-

ally undetectable. Therefore, for all prac-tical purposes, the NTT can now be re-garded as a perfectly aligned telescope.The improved optical quality of the NTThas been confirmed by subsequent ob-servers. pgitton@eso.org

The editors of the La Silla News Page would like to welcome readers of the tenth edition of a page devoted toreporting on technical updates and observational achievements at La Silla. We would like this page to inform theastronomical community of changes made to telescopes, instruments, operations, and of instrumental perform-ances that cannot be reported conveniently elsewhere. Contributions and inquiries to this page from the commu-nity are most welcome. (R. Gredel, C. Lidman)

The La Silla News Page

CES Very Long Camera InstalledM. KÜRSTER, ESO, Chile

After a general overhaul of the CoudéEchelle Spectrometer (CES), its newVery Long Camera was successfully in-stalled between April 9 and 20. It con-sists of a new f/12.5 camera mirror thatwas mounted in the frame of the oldscanner mirror and an x-y table on newpillars which hold a new 45° foldingmirror and the CCD mount. The newVery Long Camera was jointly built byUppsala Astronomical Observatory (op-tics) and the University of Liège (me-chanics). It replaces the previous Long

Camera (f/4.7) which was decommis-sioned.

During a first series of test measure-ments with the thorium-argon lamp, re-solving powers of R = 235,000 were ob-tained at different wavelengths. At thisresolving power the sampling was de-termined to be P 2.45 pixels/FWHM.

The Very Long Camera will be com-missioned during May 14–20 togetherwith the new fibre link to the Casseg-rain focus of the 3.6-m telescope andimage slicers built by ESO Garching

(optics) and ESO La Silla (mechanics).A sliding carriage with housings for upto four different image slicers has al-ready been installed. The slit unit wasalso integrated on this sledge. Theweeks before the commissioning will seethe installation of the fibre in the Cas-segrain adapter, and the installation ofthe fibre exit unit in the CES pre-slit area.The latter unit will be movable (with veryaccurate repositioning capabilities) topermit the continued use of the CAT tel-escope with the CES.

Improving Image Quality at the Danish 1.54-m Telescope

J. BREWER, ESO, La SillaJ. ANDERSEN, Copenhagen University Observatory, Denmark

The image quality achieved at a tele-scope depends on many factors, not theleast of which is the thermal environmentof the dome, telescope, and mirror. Dur-ing the daytime, the dome, telescope andmirror heat up; at night this heat is re-leased, causing air turbulence which de-grades the seeing by causing the star-light to be diffracted along different paths.As part of the seeing improvement cam-paign at the major La Silla telescopes, ithas been decided to address these prob-lems also at the Danish 1.54-m telescope,

which was once known for its excellentimages (e.g. The Messenger No. 17, p.14, 1979).

After a lengthy period of measure-ments and analysis by Danish and ESOstaff (in particular M.I. Andersen and A.Gilliotte), it was concluded that bothcharge diffusion effects in the (thinnedLoral 2K) CCD and thermal problemsnear the mirror and in the dome and build-ing were responsible for the currentlyobserved image degradation. Consider-ing that the contract between ESO and

Copenhagen University on the operationof the telescope had been extended fora ten-year period from 1996, a substan-tial investment in reducing daytime heat-ing of the dome, telescope and mirror wasfound justified.

There are two ways to address thisproblem. One solution is to estimate thenighttime temperature and to maintain thedome, telescope and mirror at this tem-perature during the daytime by use of acooling system. The other solution is toincrease the natural ventilation in the

Reference

[1] Collimation of Fast Wide-Field Telescopes,McLeod, B.A., 1996, PASP 108, 217–219.

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evening and during the night, while at thesame time reducing the radiative heat fluxfrom the concrete surfaces of the domeinterior. Both approaches have advan-tages and disadvantages, and they arenot mutually exclusive: An already partlycool dome reaches equilibrium fasterwhen ventilated, and good ventilation inthe evening and during the night reduc-es demands on the cooling system. Amain advantage of the natural ventilationapproach is, however, that it is simple toimplement, requires little maintenance,and has no significant operational cost(unlike a large refrigeration plant).

After commissioning a number of cost/benefit engineering studies, it was decid-ed by Copenhagen University Observa-tory (CUO) to implement a natural venti-lation solution by raising the entire domeby 70 cm and installing side ports in thespace between the dome and the build-ing. A similar system is already in use atthe Nordic Optical Telescope on La Pal-ma, Spain, and will be used at the newSwiss telescope at La Silla. It was agreedwith ESO that this would be supplement-ed by an effort to improve the thermal in-sulation and the performance of the ex-isting ventilation and cooling systems inthe building (which, unlike the telescopeitself and the dome, is ESO property).

The mechanical design and prefabri-cation of the dome ports was undertak-en by the Danish engineering companyRichard Thomsen A/S. The ports wereshipped to Chile and installed at the tele-scope during the period 4 April – 1 May1998 by Anders Larsen and Kjeld Olsenof Richard Thomsen A/S in collaborationwith CUO staff members Morten Jensen,

Hans Henrik Larsen, Niels Michaelsenand Preben Nørregaard.

Figure 1 is a view of the open portsseen from the inside of the dome. Theports are split into 8 sectors of 4 portseach, and it is possible to open or closeany of the sectors separately. This willallow the system to be used in strongwind conditions when wind-borne dust isof concern and the dustladen wind mustbe kept from entering the telescope build-ing. The system is mechanically simpleand should require minimal maintenance.For simplicity, it is planned initially to ap-ply the standard La Silla wind limits fordomes also to the ports; i.e., all ports mayremain open if the wind speed is less than14 m/s, while ports in the wind directionshould be closed when the wind speedis above 14 m/s. At wind speeds greaterthan 20 m/s, all ports (and, of course, thedome itself), must remain closed.

The side ports are opened and closedfrom a large control box located on thewest wall next to the telescope. Havingthe control box on the dome floor willensure that observers will not use thesystem blindly. The side ports can onlybe fully open or closed; it is not possibleto open the ports partially.

The next stage of the project is to im-prove the internal insulation of the dometo reduce the heat flow from the concretefloors and walls of the building. The insu-lation work will be carried out by the LaSilla Infrastructure Group in the next fewmonths after a final design has beenagreed upon and the materials pur-chased. Meanwhile, the ventilation sys-tem in the dome will be refurbished so asto primarily draw warm air away from the

telescope, especially from the controlroom under the observing floor. Ways willalso be investigated to use any addition-al capacity of the cooling plant above thatneeded to cool the TCS rack to reducethe daytime temperature in the dome.

In addition, with a much improved ther-mal monitoring system at several loca-tions in the telescope and dome, and withimproved access to the mirror, it is intend-ed to gradually bring the mirror coolingsystem into operation when safe ways toavoid accidental condensation of mois-ture have been worked out. In parallel,the design and operation of the mirrorventilation system will be improved, draw-ing on the very encouraging experiencefrom the ESO 3.6-m telescope. The finalstep in the process would be to replacethe CCD with one that does not sufferfrom the degradation in resolution seenwith the Loral chips, but a suitable chipwith the desired combination of high spa-tial resolution, availability and affordableprice has not yet been identified.

Additional work which has been doneduring this extended technical period in-cludes:

• Clean and bake the CCD dewar andits molecular sieve (CUO).

• Move the CCD preamplifiers to theoutside of the dewar (CUO).

• Re-aluminise and realign M1 (LSOptics Team).

• Refurbish the drive and install limitswitches for the DFOSC rotator (CUO).

• Install new, more powerful fans withair filters for mirror ventilation (CUO).

• Drill holes in the mirror cell to improvethe air flow of the mirror cooling system(CUO).

• Remove many obsolete cables andre-route many of the loose cables hang-ing from the telescope (CUO and 2p2Team).

• Remove instruments that have beendefinitively retired from active service atthe telescope (two-channel photometer,polarimeter, CORAVEL).

• Upgrade the version of VXworks forthe TCS VME (2p2 Team).

• Upgrade the workstations to HP/UX10.20 (LS Software group).

• Install 2 9-GB disks on the data-ac-quisition WS (LS Software group).

We trust that these major efforts bymany staff members of CUO and of ESOwill give this favourite workhorse of manyESO and Danish observers another longperiod of productive service, even in aworld of stiffening competition. The sub-stantial investment in the dome upgradehas been provided by the Danish Natu-ral Science Research Council through itsInfrastructure Centre for Ground-BasedAstronomy, located at CUO.

Figure 1: View of the open ports from the inside of the dome.

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The NTT Service Observing Programme: Period 60Summary and Lessons LearnedD. SILVA (dsilva@eso.org), Data Management and Operations Division

This is the second in a regular series of articles about VLT Data Flow Operations (DFO). In this article, the NTTservice observing programme, a VLT DFO prototype, is discussed.

1. Introduction

Between February 1997 and March1998, ESO ran a service observing pro-gramme at the NTT. The primary goal ofthis programme was to develop and testprototype operations tools and conceptsfor the planned VLT service observingprogramme. The NTT programme hasbeen halted for now and service ob-serving is not scheduled for Periods 61or 62. However, the Observing Pro-grammes Committee and the UsersCommittee have recommended that NTTservice observing resume during Period63, provided ESO can devote resour-ces to this programme without hinder-ing the development or implementationof VLT science operations. ESO is alsostudying what is necessary to providelimited service observing support for useof the Wide Field Imager at the 2.2-mstarting in Period 63.

Before continuing service observing atthe NTT or implementing it at other ESOfacilities, it is appropriate to ask: whathave we learned? In this article, the con-cepts and history of the NTT service ob-serving programme are described. Thensome lessons learned and how they willaffect VLT planning are discussed.

2. Why Service Observing?

When assessing the success of a pro-totype programme, it is important to keepin mind the original high level goals. Serv-ice observing (as previously discussed bySilva & Quinn, 1997) has three maingoals:

2.1 Maximise science efficiency

Service observing attempts to maxi-mise science efficiency in two ways. First,at any given moment, the highest OPCranked programme with Principal Inves-tigator (PI) specified observing conditions

requirements which match the currentobserving conditions is given highest pri-ority. In this way, the most scientificallymeritorious programmes are executedfirst and under the PI defined optimalobserving conditions. Remember, how-ever, that no matter how highly a pro-gramme is ranked by the OPC, if a PIrequests rare conditions, such as ex-ceptionally good seeing, their programmemay never be executed if those condi-tions do not arise.

A second goal is to acquire scientifi-cally useful datasets, as defined by theprogramme Principal Investigator (PI).For example, in a multi-cluster sample, itmay be more useful to have a completedataset for one cluster than randomly in-complete datasets for all clusters. Overthe course of some time interval, thesegoals should assure that the highestranked proposals are completed first aslong as they do not require rare observ-ing conditions.

A third goal is to facilitate the schedul-ing of a broader range of science pro-grammes, such as synoptic and Targetof Opportunity programmes as well asprogrammes that require co-ordinationbetween several different facilities. Suchprogrammes are difficult to support in astandard operations model.

2.2 Maximise operational efficiency

Service observing tries to maximiseoperational efficiency in two ways. First,whenever possible, scientifically appro-priate, and consistent with OPC recom-mendations, observations that requirecommon calibration data are executed asa group so that the calibration data canbe shared between several different pro-grammes. Second, experienced staffobservers are used to execute observa-tions. Since they are more familiar withthe facility, these observers should bemore efficient relative to visiting astrono-

mers who only use the facility once ortwice a year. Furthermore, most visitingastronomers, no matter how experienced,are less efficient on their first night. Forthe two- or three-day observing runs typ-ical at heavily used facilities like the NTT,this first night inefficiency can have a sig-nificant impact on the overall productivi-ty of the observing run. Staff astronomers,given their familiarity with the facility, canusually minimise this problem.

2.3 Maximise ability to re-use data

An important goal for the VLT and oth-er ESO facilities like the NTT is to maxim-ise the ability of future researchers tore-use data to address different scienceproblems. It is easy to capture all acquireddata and store them, but these data willbe worthless without suitable calibrationdata and proper records. Anecdotal evi-dence as well as a review of the NTT dataarchive suggests that many visiting as-tronomers do not perform a calibrationand operations plan rigorous enough toproduce uniform datasets for future use.During service observing, however, theobservatory has total control and can as-sure that proper calibration data are ac-quired and sufficient records kept. Thisprocess is facilitated by the implementa-tion of calibration plans for each instru-ment by the scientist responsible for thatinstrument.

3. Why the NTT?

As part of the NTT Big Bang process,ESO installed a VLT Data Flow System(DFS) prototype. The DFS is a set of soft-ware tools and procedures to manageVLT science programmes from the initialproposal to future archival research(Quinn, 1997). These tools were de-signed with the needs of both serviceobserving and visiting astronomer pro-grammes in mind.

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But do these tools work? Do they fa-cilitate or hinder service observing? Dothey make general observatory opera-tions more efficient or less efficient?These are issues that ESO wanted toaddress and resolve before VLT opera-tions began.

Furthermore, VLT science operationsare not simply a matter of implement-ing the right software and hardware.The proper procedures must also bedeveloped and documented. Some ofthe most important procedures involveproviding adequate user support, whichinvolves not only answering user que-ries and providing adequate generaldocumentation, but also providing theright level of real-time information aboutobservatory operations. Again, ESO sawthat it was better to develop these pro-cedures as early as possible, so thatVLT science operations would be asefficient as possible right from thestart.

4. Periods 58 and 59: Learning theHard Way

NTT service observing began at theNTT during February 1997. During thesecond half of Period 58 and the first halfof Period 59 (February – June 1997),service observing was executed by theNTT Team on a “shared risk” basis as BigBang activity and weather permitted. De-spite heroic efforts by the NTT Team (ledat the time by Jason Spyromilio), opera-tions were plagued by a number of tech-nical problems, as well as a particularlystrong El Niño weather pattern, reducingthe amount of useful data acquired to aminimum. To make matters worse, userswere required to come to Garching to pre-pare Observation Blocks (OBs)1, assist-

ed by the DMD User Support Group (ledby the author), using prototype software.Several frustrated users who investedmany hours in preparing OBs never re-ceived any data. Due to poor planningand bad records (e.g. faulty FITS head-ers), data quality control and distributionby the USG fell behind. Although this pe-riod had been advertised as “shared risk”and “best effort”, most users were unhap-py. Nevertheless, some interesting sci-ence programmes were successfully sup-ported, such as the SUSI Deep Fieldproject (D’Odorico, 1997) and follow-upspectroscopy of Galactic bulge microlens-ing events (Lennon et al., 1997).

The second half of Period 59 (July –September 1997) (often called NTT2 orPeriod 59.2) was supposed to be a re-turn to full NTT operations. On the moun-tain, technical operations proceededmuch more smoothly, thanks again to thehard work of the NTT Team (led then byGautier Mathys). Unfortunately, observ-ing conditions continued to be poor, es-pecially the seeing, due to the strong ElNiño effect. In Garching, although the OBcreation and scheduling process wentmuch better, USG data quality control anddistribution activity continued to be veryinefficient. Much of the Period 59.2 datawas not distributed to the proper end us-ers until December 1997, i.e. 3–6 monthsafter the data were acquired. Simply put,the USG did not have sufficient person-nel during Period 59.2 to accomplish itsassigned tasks in a timely manner.

These were painful months for every-one, users and ESO staff members alike.

Figure 1: Period 60 NTT Service Observing task flow.

Figure 2: The Period 60 NTT service observ-ing organigram. NTT service observers dur-ing Period 60 were F. Comerón, J.-F. Gon-zález, C. Lidman, M. Scodeggio, and G. vande Steene.

1Observation Blocks (OBs) describe how simple datasets are acquired and record the status of those data-sets. OBs are simple – they consist of just one telescope pointing and the acquisition of a single dataset. Theyare the smallest items that can be created, scheduled, and executed by the Data Flow System.

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5. Period 60: A New Beginning

In many ways, Period 60 representeda new beginning for the NTT service ob-serving programme. With improved soft-ware tools, adequate staffing, and im-proved weather conditions, ESO wasable to provide much better service to ourusers.

5.1 The Tasks

Figure 1 illustrates the NTT serviceobserving tasks during Period 60.

Observation Blocks (OBs) were cre-ated by PIs assigned NTT service observ-ing time using the Phase 2 ProposalPreparation (P2PP) tool. Most Period 60users were able to create their OBs attheir home institutions without significantassistance from the USG. Only one userhad to come to Garching and the USGdid create OBs for two programmes. Af-ter creation, OBs were submitted direct-ly across the Internet to ESO by the P2PPtool for scheduling.

Scheduling was a two-part process.For any given service observing run, theUSG created a Medium-Term Schedule(MTS) which contained a list of all exe-cutable OBs for the given Local SiderealTime range, lunar phase, and availableinstrumentation. The MTS also containedinformation about relative OPC priorities,user specified observation condition re-quirements, and required instrument con-figurations. Typically, the MTS was cre-ated less than 36 hours before the startof a service observing run. The secondphase of scheduling, creating the Short-Term Schedule (STS), was done by theNTT Team at the telescope. In real-time,the NTT service observer would selectan OB from the MTS pool with the high-est OPC priority which could be execut-ed under the current observing condi-tions. For most of Period 60, this wasdone manually, although during earlyFebruary 1998, a prototype STS creationsoftware tool was tested.

NTT mountain operations was the re-sponsibility of the NTT Team. Tasks in-cluded science OB selection and execu-tion, calibration plan execution, real-timedata quality checking, and a variety ofrecord-keeping tasks.

Once acquired, data were transferredback to Garching, usually immediately viaFTP transfer. The next day, all data werereviewed and classified manually usinga standardised data quality control proc-ess. Frames were graded:

• A – all user specifications met• B – all user specifications met within

25%• C – all user specifications violated

by 25% or moreIf an OB (or some part of an OB) failed

to pass data quality control, attemptswere made to re-execute it later.

Once a logical dataset was collectedfor any given programme (e.g. all obser-vations in a given filter, all observations

of a given cluster), a CD-ROM was pre-pared containing all the science data plusthe relevant calibration data. Users weresent all data taken for their programme,no matter what the quality control grade.In practice, Period 60 data were distrib-uted three times: in December 1997 whenSUSI was decommissioned (all SUSI PIswere issued whatever data were availa-ble for their programmes), in February1998, when a number of EMMI pro-grammes were completed, and in April1998 (i.e. the end of Period 60), at whichpoint all remaining data were distributed.In short, within one month of the comple-tion of Period 60, all data had been dis-tributed, a vast improvement over thePeriod 58 and 59 problems.

Finally, user information was regular-ly updated on our Web site, which is stillavailable at http://www.eso.org/dmd/usg.Information posted included nightly ac-tivity summaries and updates on theprogress of individual programmes.

5.2 The Team

Although many improved tools andprocedures were used during Period 60,the most significant improvement wasallocating the right number of people. ThePeriod 60 team is shown in Figure 2.Keeping in mind that the DMD ScienceArchive Operations team was supportingNTT and HST/ECF archive activities aswell as VLT archive operations start-up

work, the Period 60 NTT service observ-ing programme personnel cost was 2.0–2.5 Full Time Equivalents (FTEs), includ-ing all USG, NTT Team, and Science Ar-chive Operations activities.

5.3 The Results

During Period 60, we tried to quantifyas many operations processes as possi-ble so we can analyse where we hadbeen successful and where we neededto improve. Here, three examples of theinformation available are discussed.

In Figure 3, the distribution of OBgrades based on the post-observationquality control check is shown. MostGrade B OBs were observed under slight-ly worse seeing than specified, typicallybecause the seeing deteriorated duringan exposure or because these were thebest OBs available during a period ofmarginal seeing. Grade C OBs representmore serious failures: poor tracking nearthe zenith or sudden change in sky trans-parency are typical causes. Fortunately,we were able to repeat most Grade COBs. The generally high success ratewas due to the fact that OBs whichspanned a large range of observing con-ditions were almost always available.Rarely did we have problems with nothaving enough OBs for a given night.

Our records also allow us to accuratelyaccount for the time we used on the NTT.Figure 4 shows the fractional breakdown.

Figure 3: Period 60 OB Grade Distribution. Total number of science OBs executed: 495. Seetext for grade definition.

Figure 4: Period 60 Service Observing Programme NTT Time Usage. Science time = integra-tion time only. Science Overhead = slews, CCD read-down, instrument set-up. NTT Ops Over-head = focus and active optics updates. ToO Loss = time used on service observing nights forTarget of Opportunity observations (including all overheads).

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Several interesting things are revealed.First, the weather down time was only10% because during service observingruns there is almost always an OPC ap-proved programme available to take ad-vantage of worse than median seeing orreduced sky transparency. Second, the15% science overhead, is mostly EMMICCD readout time, will be more than cutin half when EMMI is upgraded to FIERAcontrollers. Finally, the NTT operationsoverheads during Period 60 were mostlycaused by inefficient telescope focus andactive optics update procedures. How-ever, these procedures have recentlybeen made more efficient – hopefully,Period 61 users have already benefitedfrom this! Finally, it is remarkable (at leastto the author) that the NTT is only suffer-ing 4% technical downtime so soon afterthe Big Bang.

A common question asked is “howmany programmes did you complete?”This issue is addressed by Figure 5.Again, this figure has several interestingfeatures. First, no SUSI programme wascompleted because: (1) many SUSI pro-grammes required excellent seeing;(2) the actual seeing was seldom sub-arcsecond during the first half of Period60; and (3) SUSI was decommissionedduring the first week of December, halt-ing SUSI operations. Second, pro-grammes with less stringent user require-ments were more successful. Finally, con-vincing the OPC to assign a high gradeis very helpful! Given this latter point, wedid not request OBs from all programmesin the low OPC priority group unless therewas a high probability that we could exe-cute some part of their programme. Ourprojections were not always accurate (i.e.some PIs submitted OBs which we nev-

er executed) but we spared some usersunnecessary work.2

6. Lessons Learned

NTT service observing has been halt-ed until at least Period 63 and ESO isnow preparing for the VLT service observ-ing programme. What have we learnedfrom the NTT experience?

6.1 Queue Management

It is important that service observingqueues span a sensible range of observ-ing conditions. For example, if on aver-age only 10% of the available time is ex-pected to have seeing less than 0.5 arc-seconds, 30% of the available timeshould not be allocated to programmesthat require such good seeing. Or, if goodbright-time instrumentation is unavaila-ble, do not assign many bright-time pro-grammes to the service observing queue.Similarly, it may be more desirable tohave a much larger relative fraction ofdark-time than bright-time assigned toservice observing if suitable bright-timeprogrammes are unavailable. Be pre-pared for abnormal conditions by over-subscribing service observing – not bynumbers of targets or hours, but by ob-serving conditions. For example, sincethe NTT usually delivers good imagequality, the ESO OPC tends to allocate alarge fraction of time to programmes thatrequire sub-arcsecond seeing. Unfortu-

nately, it was not anticipated that 1997would be a strong El Niño year and theOPC continued to allocate time to goodseeing programmes. As a result, the 1997NTT service queues contained too manysub-arcsecond seeing programmes andnot enough programmes that could tol-erate worse than arcsecond seeing.

6.2 User Information Management

Users with programmes in the serviceobserving queue typically want to knowthe following things: why is their pro-gramme not being executed right now; ifnot now, when is their programme goingto be executed; what OBs have beenexecuted to date, and when are they go-ing to receive their data. At the end of aschedule period, if their programme wasnot initiated or completed, they want toknow why. If they had been at the tele-scope, they would know the answers tothese questions (e.g. it was cloudy, therewas an instrument failure). In serviceobserving, the answers can be morecomplicated (e.g. the conditions werenever right, your programme did not havea high enough OPC scientific ranking)and sometimes the final answers are notavailable until the entire scheduling peri-od is completed.

The NTT experience demonstratesthat service observing user anxiety canbe greatly reduced by publishing the OPCrecommended scientifically ranked queueat the beginning of the period and nightlysummaries of service observing activityduring the period, including programmesserviced, observing conditions, usabletime vs. lost time, and updated summa-ries of individual programme progress. Incombination, this information allows in-dividual users to understand for them-selves why scheduling decisions havebeen made about their programme. Thebasic information desired is actually quitesimple and is easily published via theWeb (see http://www.eso.org/dmd/usg/).In addition, the VLT Data Flow Systemwill provide tools for users to retrieve in-formation about individual OBs as theirprogramme progresses.

6.3 OB Management

Philosophically, Observation Blocksare supposed to be indivisible objects.Users are instructed to keep OBs as sim-ple as possible – no more than one in-strument configuration per OB and a to-tal execution time of no more than one(1) hour, preferably as short as possible.Nevertheless, it is very tempting for us-ers to make OBs more complicated. Thismay seem more natural to users becauseduring traditional observing runs usersare familiar with the need to interrupt andre-arrange their programme in real-timeto match observing conditions. Usersexpect that service observers will do thesame. However, service observers arenot restricted to executing any particular

Figure 5: Period 60 Observing Programme Final Status Summary. For Moon (for “moon phase”),D = dark, G = gray. Under See (for “seeing”), these are upper limits on acceptable PSF FWHMin arcseconds. Under Sky (for “sky transparency”), P = photometric, C = clear, and TC = thincirrus.

2Regretfully, no data were acquired for 60.B-0711,despite having a high grade and less restrictive re-quirements, because the PI did not submit any OBs.But, of course, other programmes benefited from thisdecision.

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programme during the night. They havethe freedom to pick observations to meetconditions from a variety of programmes.To make this process efficient, serviceobservers want OBs to be as simple andas short as possible to maximise sched-uling flexibility.

Two example OBs illustrate this point:consider OBs which request N imagingintegrations through M filters of the sametarget or N 3600-second spectroscopicintegrations of the same target. Duringservice observing operations, such com-plex OBs are difficult to schedule efficient-ly. Furthermore, the schedule problem isexacerbated when part of a complex OBproduces bad data and the observationmust be re-scheduled. Since the DFS isonly supposed to re-schedule completeOBs, not parts of OBs, re-schedulingcomplex OBs reduces the overall produc-tivity of the queue.

Such inefficiencies can be avoided intwo ways. First, users must be educatedto make OBs which are easy to sched-ule, so they must be told how OBs arescheduled and given OB constructionguidelines. In the examples above, thesimplest and easiest to manage choiceswould have been M × N imaging OBs andN spectroscopic OBs. Second, the toolsfor OB construction must be able to makeOBs efficiently so the user is willing tomake many simple OBs as opposed to afew complex OBs.

6.4 Data Management

One of the most important experienc-es from the NTT is the need to reviewand distribute service observing data asquickly as possible. Timely data review,preferably the next day after a servicenight, is critical for uncovering data prob-lems (e.g. deficient calibration data, in-strument performance anomalies) earlyenough that many subsequent nights ofdata are not corrupted. Timely reviewmaximises schedule flexibility by pro-viding information about which OBs needto be re-scheduled and which pro-grammes need to be serviced (or canstop being serviced because enoughOBs have been completed). Finally,timely review also allows more rapiddata distribution. One VLT goal is tohave 90% of the data distributed withinone month of the observation execution,with the biggest anticipated bottleneckbeing the transfer of data from Paranalto Garching on digital media. Improvedtools to make data quality control ac-tivities more efficient, more informative,and more uniform, are planned forUT1.

Efficient data management also relieson correct and complete FITS headers.During the first half of 1997, the NTTheaders had a number of problems whichexacerbated our data distribution prob-lems. It is obviously critical to stabiliseFITS headers early and then rigorouslymaintain them.

6.5 Operations Management

A requirement for the success of VLTscience operations is the need toco-ordinate science operations acrosstranscontinental distances. The NTTservice observing programme demon-strated that the DFS will be able to han-dle the technical co-ordination issues.During 1997, it was possible: for OBsmade by users at their home institutionsto be submitted electronically to Garch-ing and then automatically forwarded toLa Silla; for Medium-Term Schedules tobe generated in Garching and transferredelectronically to La Silla; for operationalproblems to be resolved via e-mail; andfor acquired data to be automaticallytransferred from La Silla back to Garch-ing for ingestion into the science archive.

However, the NTT programme also il-lustrated that not all relevant informationis or can be encoded in the OBs, logs,and FITS files transferred between Chileand Germany, that real-time decisionsmust sometimes be made when the timezone difference and/or workshift inversionmake real-time communication betweenthe two groups difficult to co-ordinate; thatit is usually easier for the local team toanticipate and solve local problems thanthe remote team; and that deviations fromstandard procedures or the original planmust be globally communicated and ex-plained.

Applying these lessons to VLT scienceoperations implies a high degree of per-sonal operational awareness and respon-sibility from the members of the opera-tions teams to assure success, especial-ly by the on-duty service observer. Oneof the biggest challenges of service ob-serving is assuring that the service ob-server has enough information to makegood real-time scheduling decisions.Service observers cannot just blindly fol-low a schedule made remotely – theymust be trained and empowered to makethe right real-time decisions to use theVLT in a scientifically effective and oper-ationally efficient manner.

Clearly stated, globally communicat-ed lines of responsibility and authority arealso important for a distributed operationsmodel. Early operations efficiency at theNTT was reduced because the tasks andresponsibilities of the various sub-teamswere not sufficiently defined. By Period60, this issue had been resolved but it isunacceptable for this to happen again atthe VLT. During 1998, ESO will be work-ing on defining carefully the VLT scienceoperations roles and responsibilities, aswell as the VLT operations commandstructure.

Finally, task load must be matched toavailable resources. ESO did not ade-quately support NTT service observingduring Period 59 and the result was defi-cient user services, particularly in the areaof data distribution. We believe the VLTscience operations task and availableresources are properly matched.

6.6 Operations Tracking

Every oversight committee in the worldinterested in telescope operations wantsto have detailed statistics about serviceobserving programmes, especially inthese early days as this technique is de-veloped at ground-based observatories.It is not that they are skeptical, they arejust being cautious. Common requestsare: total integration time vs. total availa-ble time, programme completion statusvs. TAC/OPC ranking, programme com-pletion status vs. actual observing con-ditions, and relative fractions of opera-tional overheads, calibration observa-tions, technical downtime, weather-relat-ed downtime, and science observations.Other combinations are possible.

It is far better to anticipate these re-porting requirements early and build upthe statistical databases progressivelyduring operations than to try to recoverthis information from observing logs,e-mail, OBs, etc. after the fact. Althoughnot an explicit design requirement, as aby-product of operations, the Data FlowSystem generates all the relevant rawinformation. Tools for automatically gen-erating the anticipated reports areplanned.

7. Conclusions

We conclude with the obvious ques-tion: did we achieve our original high-levelgoals at the NTT as stated at the begin-ning of this article? In the area of scienceefficiency, as Figure 5 illustrates, we didconcentrate on more highly ranked pro-grammes and we were successful atcompleting programmes we executed.We were also operationally efficient (seeFigures 3 and 4) – we were able to mini-mise weather down-time, most of the timewe only had to execute an OB once toacquire data acceptable to the user, andwe did share calibration data betweenprogrammes (although only for imagingprogrammes). Finally, because we didhave a standard calibration plan and wedid execute it faithfully, the data deliveredto the archive should be quantitativelyuseful to archival researchers once thedata become public.

However, other questions are impor-tant as well. Was service observing moreor less efficient than standard visiting as-tronomer observing? Are the PIs who re-ceived data satisfied with their data andhas it made them more productive? Doesservice observing increase or decreasethe science impact of the NTT? ESO willtry to answer the first question by ana-lysing records from visiting astronomerruns. The second question will be ad-dressed later this year via a survey of PIsassigned service observing time. The fi-nal question will only be answered overtime as we see what and how many pa-pers derived from service observing pro-grammes are published in the scientificliterature.

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In the end, ESO made mistakes dur-ing the Period 58–60 NTT service observ-ing programme, but we also learnedmany valuable lessons. VLT science op-erations will benefit significantly from thisinitial prototype programme.

In the next article of this series, theOB creation process will be discussed.

8. Acknowledgements

The NTT service observing pro-gramme was a team effort. During thisprogramme, the NTT Team was lead byJason Spyromilio and Gautier Mathys,both of whom contributed enormousamounts of their time and energy into this

programme. Significant service observ-ing support and operations feedback wasprovided by the following NTT Teammembers: Fernando Comerón, Jean-François Gonzalez, Chris Lidman, PierreMartin, Marco Scodeggio, and Griet vande Steene. In Garching, NTT Data FlowOperations support came from the follow-ing DMD User Support Group members:Carlo Boarotto, A. Maurizio Chavan, GinoGiannone, Steve Roche; Petia Andree-va, Fabio Bresolin, Rodrigo Ibata, andPatrick Woudt. Data Flow Operationssupport also came from the DMD ScienceArchive Operations Team: Benoit Pi-renne, Susan Hill, and Fabio Sogni. Asalways, Bruno Leibundgut struggled val-iantly to keep us on the True Path. Spe-

cial thanks to Stephanie Cote, and espe-cially, Albert Zijlstra who contributed somuch during the grim, early days.

Extra special thanks to all the astron-omers who were awarded NTT ServiceMode time during P58–P60. Hopefully, allyour hard work has paid off in useful NTTdata now and better VLT science opera-tions in the future.

References

D’Odorico, S. 1997, The Messenger, 90, 1.Lennon, D.J., Mao, S., Reetz, J., Gehren, T.,

Yan, L., and Renzini, A. 1997, The Mes-senger, 90, 30.

Quinn, P. 1997, The Messenger, 84, 30.Silva, D. and Quinn, P. 1997, The Messenger,

90, 12.

SOFI Infrared Images of the ‘NTT Deep Field’

Figure.1: Ks (2.16 µm) image of the NTT DeepField. The field is p 5 × 5 arcmin, seeing isp 0.75 arcsec and the 3σ limiting magnitudein a 1.5 arcsec diameter aperture is 22.87 (datareduced by P. Saracco).

Deep infrared J (1.25 µm) and Ks(2.16 µm) band images of a 5 × 5 arcminfield centred on 12h 05m 26s; −07 43 27(J2000) obtained during the commission-ing of SOFI (Moorwood, Cuby and Lid-man, 1998, The Messenger, 91, 9 ) atthe NTT in March 1998 will be made avail-able via the Web (under Science Activi-ties on ESO’s Homepage) in early June.The Ks image is shown here in Figure 1.This field contains the smaller region ob-served with SUSI (D’Odorico, 1997, TheMessenger, 90, 1) for which visible im-ages are already available on the Web.The infrared images have been construct-ed from jittered observations totalling 4.3hours in J and 10.4 hours in Ks and havean average point source FWHM of about0.75 arcsec. Limiting magnitudes (3σ with-in a 1.5 arcsec diameter aperture) are J= 24.66 and Ks = 22.87. Full details ofthe observations and data reduction willbe put on the Web together with instruc-tions for retrieving the images.

A. MOORWOOD

26

OBSERVATIONS WITH THE UPGRADED NTT

Upgraded NTTProvides Insights Into the Cosmic Big BangP. BONIFACIO and P. MOLARO, Osservatorio Astronomico di Trieste, Italy

The EMMI spectrograph with theupgraded NTT has been used to detectfor the first time the Li I subordinate dou-blet at λλ 6104 Å (the doublet has threecomponents: 22P1/2 – 32D3/2, 22P3/2 –32D5/2, 22P3/2 – 32D3/2, at wavelengths6103.538 Å, 6103.649 Å, 6103.664 Årespectively) in the prototype populationII star HD 140283. The Li abundancefrom this line is consistent with that pre-viously obtained from the widely usedresonance line, thus giving confidencein the use of Li in the framework ofstandard nucleosynthesis (Bonifacioand Molaro, 1998).

On August 10 and 11, 1997, we wereconducting an observing programme atLa Silla, Chile, aimed at very precisemeasures of the Li I resonance line atλλ 6707 Å in a sample of halo dwarfs.On each night we observed HD 140283for 40 and 20 minutes, respectively, as acalibration star since this is a very bright(V = 7.24) and metal poor ([Fe/H] P–2.7) star. The telescope was the ESONTT and the spectrograph was EMMIequipped with the R4 (i.e. tan θ = 4)echelle grating ESO #14 (D’Odorico andFontana, 1994 ). The seeing in thosenights was sub-arc-second and we useda projected slit width of 0.8″, obtaining aresolution of λ/∆λ P 61000, as measuredfrom the Th-Ar lamp emission lines. Ascross-disperser we employed grism # 6which achieves a wide-order separationallowing to keep a slit height of 15″ pro-jected on the sky. Such a high slit is es-sential for a good sky subtraction. Afterfull reduction with the MIDAS echellepackage the coadded spectrum had asignal-to-noise of P 360.

On such high resolution, high S/Nspectra we searched for the Li I 22P –32D, 6104 Å transition. This transition isthe strongest subordinate line of Li I but ismuch fainter than the resonance line. Sofar this line has been detected only inyoung T Tauri stars (Hartigan et al., 1989)and Li-rich giants (Wallerstein andSneden, 1982), were Li is about 1 dexmore abundant than in Population II starsowing to the Galactic Li production. Ascan be seen in Figure 1, the Li I feature isclearly detected in the spectrum of HD140283 at 6103.6 Å, redwards of theCa I 6102.723 Å line, in the photosphericrest frame. The equivalent width is 1.8 ±0.3 mÅ and the detection is at 6σ of con-fidence level.

This detection is clearly a credit to thehigh-resolution capabilities of the NTT,

and its improved efficiency allowed us toperform the observations in a reasona-ble amount of time; however, what is itsastrophysical significance? Lithium, to-gether with D and 3,4He, is one of the fewelements produced by nuclear reactionsin the first minutes after the big bang(Wagoner, Fowler and Hoyle, 1967). Theobservations of these elements and theirextrapolation to the primordial values areabout consistent with the predictions ofthe primordial nucleosynthesis providing,together with the relic radiation and theexpansion of the Universe, a robust sup-port to the standard big-bang theory(nothing to do with NTT here). Since theyields of light elements depend on thesingle parameter η = nb/nγ, the baryon tophoton ratio, the determination of the pri-mordial Li abundance, as well as the oth-er primordial elements, allows us to fixthe value of η, and therefore of Ωb. Thepossibility to determine the primordialabundance of Li relies on the discoverymade by Spite & Spite (1982) that metal-poor halo dwarfs showed the same Liabundance regardless their metallicity oreffective temperature: the so-called Spiteplateau. This was interpreted as evidencethat the Li observed in these stars was ofprimordial origin. Recently, additionalsupport to the primordial nature of Li inhalo dwarfs has come from the observa-tions of Li in metal-poor stars of the thickdisk (Molaro, Bonifacio and Pasquini,

1997). This population is chemically andkinematically distinct from the halo, buthas the same Li abundance as the halo.Minniti et al. (1997) claimed detection ofLi, at the plateau level, in a metal-rich,but old star, belonging to the GalacticBulge. Finally, Li at the plateau level hasalso been detected in a star which waspossibly born in an external galaxy andthen accreted by the Milky Way (Molaro,1997).

So far the Li abundance has alwaysbeen obtained only from the analysis ofthe Li I λλ 6707 Å resonance doublet.This is not a very comfortable situation.Quite seriously, our ability to determinethe Li abundance using simple plane-parallel homogeneous atmospheres, hasbeen challenged by Kurucz (1995). Theanalysis of several lines, which sampledifferent depths in the stellar atmos-phere is crucial to test the correctnessof the modelling. The one-dimensional,homogenous, static models which arecurrently employed may arise concernbecause they ignore the fine structureand hydrodynamic phenomena such asgranulation which are seen on the Sun.The detection of the Li I λλ 6104 Åtransition in the spectrum of the metal-poor star HD140283 opens up for thefirst time the possibility of testing theapplicability of our simple models to thedetermination of Li abundances. Wehave verified that both the subordinate

Figure 1: The observed Li I 22P – 32D transition.

27

and the resonance line are consistentwith the computations made using aone-dimensional, homogeneous modelatmosphere, thus increasing our confi-dence that this model represents a sat-isfactory average of the complex finestructure expected in metal-poor stars(Bonifacio and Molaro, 1998). The VLTand the high-resolution capabilities ofthe UVES spectrograph will allow tomeasure the Li 6104 Å Li I subordinatedoublet in other much fainter population IIstars, thus permitting to verify the con-sistency between the resonance andsubordinate Li I lines on a statisticallysignificant sample, thus achieving a moreaccurate measurement of the primordialLi abundance and ultimately of Ωb.

In addition to the problems with the Liabundance determination, one must becareful about two other possible effectswhich are important in this context: Li pro-duction by galactic sources and Li deple-tion in the stars. Consider Li productionfirst: we know that the meteoritic value is(Li/H) = (2.04 ± 0.19) × 10–9, i.e. over oneorder of magnitude larger than that ob-served in the Pop II stars. Several mech-anisms may contribute to raise the Liabundance from the Pop II value to themeteoritic value like spallation by cosmicrays in the ISM, production in AGB stars(Cameron-Fowler mechanism) or neutri-no-induced nucleosynthesis in superno-va explosions. There are several uncer-tainties in the various contributions, but itseems that there are no problems for aGalactic Li production of the order of 90%of the Li presently observed (MatteucciD’Antona and Timmes, 1995). ConsiderLi depletion next: Li is a very fragile ele-ment and can be destroyed if convectiontakes it down to temperatures of about2.6 × 106 K where the Li(p,α)He reactionis effective. This is what probably hap-pened in the sun where the Li abundancein the solar photosphere is two orders ofmagnitude less than the meteoritic val-

ue, and in solar metallicity field stars whichshow a scatter in the Li abundance ofthree orders of magnitude. For Pop IIstars the situation is remarkably different.The Spite plateau shows no evidence forscatter in Li abundance (Bonifacio andMolaro, 1997). The surface convectionzone of a metal-poor star is much shal-lower and more superficial than that of asolar-metallicity star of the same effec-tive temperature probably preventing Lidestruction. Standard models predict noLi depletion for metal-poor stars. Deple-tion is predicted by non-standard modelswhich take into account rotational mixingor diffusion (Pinsonneault, Deliyannis andDemarque, 1992, Vauclair and Charbon-nel, 1995). However, these models pre-dict a downturn of the hot side of the Liplateau and considerable dispersion,which are not seen in the observations.This suggests that diffusion or rotationalmixing do not affect significantly the Liobserved at the stellar surface ofmetal-poor dwarfs.

Overall, the case for a primordial lithi-um at the value observed in the Popula-tion II stars, with no production by galac-tic sources or destruction inside the stars,is rather robust. The primordial yields forLi are not a monotonic function of η, dueto the different contribution of the Li form-ing reactions at different η regimes. Theyshow a minimum, i.e. the Li valley. Thisimplies that in general a value for Li willprovide two solutions for η. Only knowl-edge of the primordial abundance of theother light elements allows to rule out oneof the two roots. The more recent valueis (Li/H) = 1.73 ± 0.05stat ± 0.2syst × 10–10

(Bonifacio and Molaro, 1997), whichgives two different values for η: η = 1.7 ×10–10, which is in agreement with the highdeuterium (D/H = 2.0 × 10–4 Webb et al.,1997) and the low primordial helium (Y =0.228 Pagel et al., 1992) and η = 4.0 ×10–10 which is in much closer agreementwith the low deuterium (D/H = 3.4 × 10–5

Burles and Tytler, 1998) and relativelyhigh primordial helium (Y = 0.243 Izotovet al., 1997). Thus a perfect concordanceon the η value derived from the observa-tions of the primordial elements has stillto be found.

References

Bonifacio P. & Molaro P., 1997, MNRAS, 285,847.

Bonifacio P. & Molaro P., 1998, ApJL, in press.Burles S., & Tytler D., 1998, in Primordial Nu-

clei and their Galactic Evolution. ISSI work-shop, Kluwer, Dordrecht, preprint astroph/9712265.

D’Odorico S. & Fontana A., 1994, The Mes-senger, 76, 16.

Hartigan P., Hartmann, L., Kenyon S., Hewett,R. & Stauffer J., 1989 ApJS, 70, 899.

Izotov Y., I., Thuan T., X., Lipovetsky: 1997,ApJS 108, 1.

Kurucz, R.L., 1995, ApJ, 452, 102.Matteucci F., D’Antona F., and Timmes, F. X.

1995 A&A 303, 460.Minniti D., Vandehei T., Cook K. H., Griest K.,

& Alcock C., 1997, submitted to ApJ,astro-ph/9712047.

Molaro P., 1997, in D. Valls-Gabaud, M.A.Hendry, P. Molaro, and K. Chamcham, eds.,ASP Conference Series, Vol. 126, 1997, p.103–120.

Molaro P., Bonifacio P., & Pasquini L., 1997,MNRAS, 292, L1.

Pagel B.E.J., Simonson E. A., Terlevich R., J& Edmunds M. G. 1992, MNRAS, 255, 325.

Pinsonneault M.H., Deliyannis C.P., & De-marque P., 1992, ApJs, 78, 179.

Spite, F. & Spite, M., 1982, A&A 115, 357.Vauclair S., & Charbonnel C., 1995, A&A, 295,

715.Wagoner R.A., Fowler A., & Hoyle F., 1967,

ApJ, 148, 3.Wallerstein G., & Sneden C., 1982, ApJ 255,

577.Webb J.K., Carswell R.F., Lanzetta K.M., Ferlet

R., Lemoine M., Vidal-Madjar A., & BowenD. V., 1997, Nat, 388, 250.

Ground-Based Detection of the Isolated Neutron StarRX J185635-3754 at V = 25.7 Mag with the Upgraded NTTR. NEUHÄUSER

1, H.-C. THOMAS 2, F.M. WALTER

3

1MPI Extraterrestrische Physik, Garching, Germany, rne@mpe.mpg.de2MPI Astrophysik, Garching, Germany3Department of Physics and Astronomy, SUNY, Stony Brook, USA

We report the first ground-based detection of the isolated, non-pulsating neutron star RXJ185635-3754 at V = 25.7 mag,obtained with the upgraded NTT in August 1997. This object has been detected first as ROSAT source and was subsequentlyidentified as neutron star with the HST. It is located foreground to a dark cloud, i.e. at a distance of less than 130 pc. Withfuture VLT observations, we may be able to measure its parallax.

The unidentified ROSAT X-ray sourceRXJ185635-3754 has been claimed tobe an isolated (i.e. not in a binary

system) old neutron star (NS), because(1) it shows constant X-ray emissionboth on short time-scales (no pulses)

as well as on long time-scales, havingbeen detected by the Einstein Observa-tory Slew Survey, the ROSAT All-Sky

P. Bonifaciobonifaci@oat.ts.astro.it

28

Survey, and in ROSAT PSPC and HRIpointed observations with very similarfluxes; (2) it is a very bright (3.7 ROSATPSPC cts/sec) source with a very soft(kT = 57 eV blackbody) spectrum, asexpected for an old NS; (3) no opticalcounterpart could be found down to VQ 23 mag; and (4) the source appearsto be projected towards the R CrA darkcloud located in Corona Australis at Q130 pc, and the column density fromthe PSPC pointing places the sourceforeground to this cloud (Walter et al.,1996).

By re-evaluating the boresight cor-rection of the ROSAT HRI observation,and identifying another source in thesame HRI field of view with a coronallyactive T Tauri star by using the B&Cspectrograph at the ESO 1.52-m tele-scope, we have revised the X-ray posi-tion and its error circle (Neuhäuser etal., 1997). Then, a very faint star wasdetected in this new error circle with theHST WFPC2 with 25.6 mag at F606 Q Vand 24.4 mag at F303 Q U (Walter &Matthews, 1997). Hence, this star isvery blue, suggestive of the hot surfaceexpected in a NS.

This object is the first example ofthe long-sought isolated, non-pulsatingNS, of which there should be p 108 to109 in the Galaxy, based on pulsarbirth-rates and the metallicity in theinterstellar medium. Its X-ray emissionis due to either accretion from the am-bient interstellar material (old NS) or acooling surface (middle-aged NS). SinceBondi-Hoyle accretion scales with υ–3,measurement of its velocity υ will ena-ble us to distinguish between thesealternatives. Also, since it is an isolat-ed (i.e. single) object, we can reallystudy the surface and atmosphere of aNS.

ESO had allocated the grey night of1997 August 9/10 at the NTT for thedetection of the optical counterpart (pro-gramme 59.D-0580, PI Neuhäuser), i.e.shortly after the start of normal opera-tion following the NTT “big bang” up-grade. The night was photometric, butthe seeing conditions (varying between1.1 and 1.4 arc seconds during expo-sures in V) required us to use EMMIinstead of SUSI. We used the EMMIred CCD #36, first with the ESOV-band filter #606, then with the ESOR-band filter #608. We also observedLandolt standard star fields throughoutthe night.

We took several images to reducethe risk of cosmic-ray contamination andplaced the expected target position ontoslightly different areas on the chip ineach exposure to avoid problems withbad pixels. After bias and flat-field cor-rection, we added the images usingstandard MIDAS procedures to constructthe final V-band image with a total ex-posure time of 150 minutes. This imageis shown in the figure (background fieldstars are labelled as in Neuhäuser et

al., 1997, IONS indicates the location ofthe detected Isolated Old NS). The NSis clearly detected with a S/N of 18inside the ROSAT error circle. The mag-nitude is V = 25.70 ± 0.22 mag meas-ured with the MIDAS command magni-tude/circle (and V Q 25.72 mag with theMIDAS Romafot package).

In addition, we have obtained imag-es at the Cron-Cousins R-band with atotal exposure of two hours towards theend of the night at air masses between1.20 and 1.28 and seeing between 1.5and 1.9 arc second. We could not de-tect the object down to R Q 24.5 mag.The broad-band spectrum (X-ray andoptical data from ROSAT, HST, andNTT) shows that the optical fluxes lieabove the extrapolated pure blackbodyand can best be fit with a Silicium-ashmodel atmosphere; in the Si-ash mod-el, the NS surface composition is madeup of 68% Fe-group elements, 11% Si,and 10% S, which is expected if asignificant fraction of the mass was ac-creted by material falling back after thecore collapse. More observations areplanned for the near future to obtain thespectral energy distribution in the opti-cal. ESO has allocated for us one darknight in July 1998 for more observa-tions of this NS with the NTT-SUSI2 (PINeuhäuser), where we plan to measurethe fluxes in B and R, and to obtain a

new detection in V for measuring theproper motion.

Observations with FORS1 at the VLTUT1 can provide an optical spectrum.Measuring its parallax should be feasi-ble on a time-scale of up to a fewyears, since the object is located fore-ground to the CrA dark cloud, i.e. atl 130 pc. Together with its X-ray fluxand emitting area, we can then deter-mine the radius of this NS. ForthcomingX-ray observations with AXAF and XMMcan provide us with its surface gravity,so that we can, for the first time, obtainthe mass of an isolated NS. This willconstrain the equation of state of de-generate matter.

Acknowledgement

We are very grateful to the whole NTTteam and in particular would like to thankGriet Van der Steene for her great helpduring our NTT run.

References

Neuhäuser R., Thomas H.-C., Danner R.,Peschke S., Walter F.M., 1997, Astron. &Astrophys., 318, L43–L46.

Walter F.M., Wolk S.J., Neuhäuser R., 1996,Nature, 379, 233–235.

Walter F.M. & Matthews L.D., 1997, Nature,389, 358.

29

RXJ0911.4+0551: A Complex Quadruply ImagedGravitationally Lensed QSOI. BURUD

1, F. COURBIN 1, 2, C. LIDMAN

3, G. MEYLAN 4, P. MAGAIN

1,*, A.O. JAUNSEN 5, 6,

J. HJORTH 6, 7, R. ØSTENSEN 1, 8, M.I. ANDERSEN 9, J.W. CLASEN 9, R. STABELL5, 6, S. REFSDAL5, 6, 10

1Institut d’Astrophysique, Université de Liège, Belgium2URA 173 CNRS-DAEC, Observatoire de Paris, Meudon, France3European Southern Observatory, Santiago, Chile; 4European Southern Observatory, Garching, Germany5Institute of Theoretical Astrophysics, University of Oslo, Norway6Centre for Advanced Study, Oslo, Norway ; 7NORDITA, Copenhagen, Denmark8Department of Physics, University of Tromsø, Norway9Nordic Optical Telescope, St. Cruz de La Palma, Canary Islands, Spain* Maître de Recherches au Fonds National Belge de la Recherche Scientifique

1. Introduction

Deriving cosmological parameters haslong been the motivation for the de-velopment of many observational tests.These parameters, including the trouble-some Hubble parameter, H0, can be de-rived from different methods, e.g., moni-toring of Cepheids in nearby galaxies, theuse of the Tully-Fisher relation or, at high-er redshifts, the photometric monitoringof supernovae. Another method to deter-mine H0, independently of these classi-cal methods, is to measure the time de-lay between the gravitationally lensedimages of QSOs. However, a good knowl-edge of the geometry of the lensed sys-tem is mandatory in order to make use ofthis information. Unfortunately, this israrely the case, in many lensed QSOsthe main deflecting mass is not even de-tected.

This was the background for a deepIR imaging project started at ESO in 1996with the 2.2-m telescope, with the prima-ry aim of detecting possible high-redshiftgalaxy clusters in the vicinity of knownmultiply imaged QSOs, as well as themain lensing galaxy. Observing in the IRoptimises the contrast between low-zfield galaxies and higher z cluster mem-bers, since the latter have their 4000-Åbreak, typical for galaxy spectra, redshift-ed into the IR for z M 0.8−1. Therefore,near-IR observations make easier thediscrimination between field galaxies andhigh-redshift cluster members.

Near-IR (1 to 2.5 microns) observa-tions have the further advantage that therelative brightness between the lensedQSO and any lensing galaxy decreases,making the galaxy easier to detect. Thedisadvantage is that the sky is consider-ably brighter in the IR than in the optical,and one is forced to take many short-ex-posure images to avoid detector satura-tion. Nevertheless, the image deconvo-lution technique developed by Magain,Courbin & Sohy (1997, 1998; hereafterMCS) allows one to take advantage ofthe numerous dithered frames obtainedand to combine them into a single deepsharp image.

Successful results have already beenobtained from this project, e.g., the de-tection of the deflector in the gravitation-al lens HE 1104-1805 (Courbin, Lidman& Magain, 1998), also confirmed byRemy, Claeskens, Surdej et al. (1998).

In this paper we report the detectionof four QSO images in the recently dis-covered lensed QSO RX J0911.4+0551.With a maximum angular separation of3.1″, it is the quadruply imaged QSO withthe widest-known angular separation.

RX J0911.4+0551, was selected as anAGN candidate from the ROSAT All-SkySurvey (RASS) (Bade et al., 1995, Hagenet al., 1995), and was recently classifiedby Bade et al. (1997; hereafter B97) as anew multiply imaged QSO. The lensedsource is a radio quiet QSO at z = 2.8.Since RASS detections of distant radioquiet QSOs are rare, B97 pointed out thatthe observed X-ray flux might originatefrom a galaxy cluster at z M 0.5 withinthe ROSAT error box.

We present here our first observationsof RX J0911.4+0551 at the 2.2-m ESO/MPI IRAC 2b in K-band which made ussuspect that the QSO might be quadru-ple. This was confirmed on our opticaldata from the 2.56-m Nordic Optical Tele-scope (NOT, La Palma, Canary Islands,Spain), and on the NTT/SOFI data of theobject (Moorwood, Cuby & Lidman,1998). Careful deconvolution of the dataallows us to clearly resolve the object intofour QSO components and a lensing gal-axy. In addition, a candidate galaxy clus-ter has been detected in the vicinity ofthe four QSO images. We estimate itsredshift from photometric analysis of itsmembers.

2. Observationsand Deconvolution

As a part of our near-IR imagingproject of gravitational lenses, RXJ0911.4+0551 was first observed in theK-band with IRAC 2b mounted on theESO/MPI 2.2-m telescope on November12, 1997. The data were processed asexplained in Courbin, Lidman & Magain(1998), and they were deconvolved us-

ing the MCS algorithm. During the decon-volution process, the sampling of the im-ages was improved, i.e., the adopted pix-el size in the deconvolved image is halfthe pixel size of the original frames. Thedeconvolution procedure decomposesthe images into a number of Gaussianpoint sources plus a deconvolved numer-ical background, and the quality of theresults is checked from the residualmaps, as explained in Courbin et al.(1998a,b). In spite of the poor seeingconditions (1.3″), preliminary deconvolu-tion of the data made it possible to strong-ly suspect the quadruple nature of theobject (see Fig. 1). From the observedimage with a seeing of p 1.3″ only twoseparated components are resolved, oneof them being elongated, suggesting thatit is a blend of two or more images. Thedeconvolution programme was run oncewith three sources and then with fourpoint sources (shown in the middle andbottom panel respectively in Figure 1).The residual maps, in units of the stan-dard deviation in each pixel, indicate thatthe solution with four point sources givesa better χ2-fit to the data. Note also thateven on these poor seeing data the de-convolution algorithm allowed us to sus-pect not only a quadruply imaged QSO,but also the presence of a lensing gal-axy.

Much better optical observations wereobtained at the NOT. Three 300s expo-sures through the I filter, with a seeing ofp 0.8″ were obtained with ALFOSC un-der photometric conditions on November16, 1997. Under nonphotometric, but ex-cellent seeing conditions (p 0.5−0.6″),three 300s I -band exposures, three 300sV-band and five 600s U -band exposureswere taken with HIRAC on the night ofDecember 3, 1997.

These high-resolution data resolvedthe object into four components andclearly confirmed our preliminary IR-results from the ESO/MPI 2.2-m tele-scope.

RX J0911.4+0551 was also the firstgravitational lens to be observed with thenew wide-field near-IR instrument SOFI,mounted on the ESO 3.5-m NTT (Moor-

30

wood, Cuby & Lidman, 1998). ExcellentK and J images were taken on Decem-ber 15, 1997, and January 19, 1998 re-spectively. The 1024 × 1024 Rockwelldetector was used with a pixel scale of0.144″. These data were processed asthe ones from the 2.2-m, but in a much

more efficient way since the array usedwith SOFI is cosmetically superior to thearray used with IRAC 2b.

All these images were also decon-volved and the final resolution adoptedin each band was chosen according tothe signal-to-noise (S/N) ratio of the data,

the final resolution improving with the S/N. The deconvolution of NOT and SOFIframes are shown in Figure 2. Not onlythe quadruple configuration of the QSOis revealed but also the main lensing gal-axy, as already suspected from our pre-liminary observations from the 2.2-m tele-scope, clearly confirming the lensing na-ture of this object.

3. Photometry

The flux ratios and positions of eachQSO component relative to the brightestone (A1) as derived from the simultane-ous deconvolutions are listed in Table 1.The position of the galaxy, also displayedin Table 1, was determined from the first-order moment of the light-distribution inthe deconvolved numerical background.The galaxy is elongated in the I-band. Inthe near IR, it looks like an edge-on spi-ral, composed of a bright sharp nucleusplus a diffuse elongated disk. However,we can not exclude that the observedelongation is due to an unresolved blendof two or more intervening objects. Deep-er observations will be required to per-form precise surface photometry of thelens(es) and to draw a definite conclu-sion about its (their) morphology. Theposition angle of the major axis of thelensing galaxy is almost the same in theI, J and K bands: PA Q 140°± 5.

In order to detect any intervening gal-axy cluster which might be involved in theoverall lensing potential and contributingto the X-ray emission observed by RO-SAT, we performed I, J and K band pho-tometry on all the galaxies in a 2.5′ fieldaround the lensed QSO. Aperture pho-tometry was carried out using the SEx-tractor package (Bertin & Arnouts, 1996).

Table 1: Flux ratios and astrometric properties relative to component A1. Positions are defined positive to the North and West of A1. All measure-ments are given along with their 1σ errors.

A1 A2 A3 B G

FK 1.000 ± 0.001 0.965 ± 0.013 0.544 ± 0.025 0.458 ± 0.004 –FJ 1.000 ± 0.002 0.885 ± 0.003 0.496 ± 0.005 0.412 ± 0.005 –FI 1.000 ± 0.017 0.680 ± 0.013 0.398 ± 0.002 0.420 ± 0.003 –FV 1.000 ± 0.007 0.587 ± 0.009 0.334 ± 0.004 0.413 ± 0.006 –FU 1.000 ± 0.003 0.590 ± 0.013 0.285 ± 0.007 0.393 ± 0.004 –x(″) 0.000 −0.259 ± 0.007 +0.013 ± 0.008 +2.935 ± 0.002 +0.709 ± 0.026y(″) 0.000 +0.402 ± 0.006 +0.946 ± 0.008 +0.785 ± 0.003 +0.507 ± 0.046

Figure 1: [Top:] Observed image from 2.2-mESO/MPI IRAC 2b; [Middle:] Result from de-convolution with three point sources to the leftand residual map to the right. The centre ofthe residual map has typical values of the or-der of 2σsky per pixel. [Bottom:] Same as abovebut with four point sources. All the values inthe residual map are now close to σsky, show-ing that 4 point sources are needed to fit thedata. The field is 9″ on a side, North is to thetop and East is to the left in all the frames.This figure is to be compared with Figure 2.Note how well the lensing galaxy shows up inthe deconvolution.

31

The faintest objects were selected tohave at least 5 adjacent pixels above1.2σsky, leading to the limiting magnitudes23.8, 21.6 and 20.0 mag/arcsec2 in the I,J and K bands respectively. The faintestextended object measured in the differ-ent bands have a magnitude of 23.0, 22.0and 20.3 (I, J and K).

A composite colour image was alsoconstructed from the frames takenthrough the 3 filters, in order to directlyvisualise any group of galaxies with sim-ilar colours, and therefore likely to be atthe same redshift. The colour compositeis presented in Figure 3. The marked cir-

cle indicates a candidate galaxy clustercentred on a double elliptical, with thesame colour as the main lensing galaxy.In addition, a group of even redder gal-axies is seen a few arcseconds to the leftand to the right of the marked cross.

4. Discussion

Thanks to our first observations fromthe 2.2-m telescope and the MCS decon-volution algorithm, RX J0911.4+0551 wasresolved into a quadruply imaged QSO,and a lensing galaxy. Furthermore, thesepreliminary results were confirmed by

high-resolution optical data and newnear-IR data from SOFI, thus clearly con-firming the lensed nature of the system.The image deconvolution provides pre-cise photometry and astrometry for thissystem.

Reddening in components A2 and A3relative to A1 is observed from our U, Vand I frames that were taken within threehours on the same night. The absenceof reddening in component B and the dif-ference in reddening between compo-nents A2 and A3 suggest extinction bythe deflecting galaxy. Note that althoughthe SOFI data were obtained from 15days to 6 weeks after the optical images,they appear to be consistent with theoptical fluxes measured for the QSO im-ages, i.e. flux ratios increase continuouslywith wavelength, from U to K, indicatingextinction by the lensing galaxy.

The observed orientation of the gal-axy, together with the asymmetric imageconfiguration, makes it difficult to modelthe lensing potential without includingexternal shear from a nearby mass. If thelensing effect was only due to a symmet-ric galaxy, whose mass distribution isroughly aligned with the light, we shouldhave observed a symmetric configurationof the QSO images about the axis throughA2 and B.

A good galaxy cluster candidate hasbeen detected in the vicinity of RXJ0911.4+0551 from field photometry inthe I, J and K bands. Comparison of ourcolours and magnitudes with that of ablank field (e.g., Moustakas et al., 1997)shows that the galaxies around RXJ0911.4+0551 are redder than field-gal-axies at an equivalent apparent magni-tude. Furthermore, several of the galax-ies are grouped in the region around adouble elliptical at a distance of p 38″and a position angle of p 204° relative toA1 (see the circle in Fig. 3).

There is considerable evidence for atleast one galaxy cluster in the field. Theredshift of our best cluster candidate (theone circled in Fig. 3) can be estimatedfrom the I and K band photometry. Wehave compared the K-band magnitudesof the brightest cluster galaxies with theempirical K magnitude vs. redshift rela-tion found by (Aragon-Salamanca et al.1998). We find that our cluster candidate,with a brightest K magnitude of p 17.0should have a redshift of z p 0.7. A sim-ilar comparison has been done in theI-band without taking into account galaxymorphology. We compare the mean Imagnitude of the cluster members withthe mean magnitude found by Koo et al.(1996) for galaxies with known redshiftsin the Hubble Deep Field and obtain acluster redshift between 0.6 and 0.9. Fi-nally, comparison of the I – K colour ofthe cluster members with data and mod-els from Kodama et al. (1998) confirm theredshift estimate of 0.6−0.8.

Some 10″ away from the lens, a groupof even redder objects can be seen (closeto the cross in Fig. 3). These galaxies

Figure 2: High-resolution images of RX J0911.4+0551 are displayed in the left panels togetherwith their deconvolved versions with improved resolution and sampling in the right panels. Ineach band, the individual data frames are deconvolved simultaneously. [Top:] Stack of 3NOT+HIRAC I-band image. The total exposure time is 900s. [Middle:] Stack of 9 NTT+SOFIJ-band frames. The total exposure time is 1080s. [Bottom:] Stack of 19 NTT+SOFI K-band witha total exposure time of 2400s. For all three bands the object is clearly resolved into four QSOimages plus the elongated lensing galaxy. The fields of the optical and near IR data are respec-tively 7″ and 9″ on a side. North is to the top and East is to the left in all the frames.

32

might be a part of a second galaxy groupat a higher redshift.

The colour of the main lensing galaxyis very similar to that of the cluster mem-bers, suggesting that it might be a mem-ber of the cluster. However, internal red-dening and inclination effects, in case itis a spiral galaxy, might bias the colourinterpretation. Given the brightness of thenucleus of the lens in K, we cannot ruleout the possibility of a fifth central imageof the source, as predicted from lens the-ory. Near-IR spectroscopy is needed toget a redshift determination of the lensand show whether it is blended or not witha fifth image of the source.

RX J0911.4+0551 is a new quadruplyimaged QSO with an unusual image con-figuration. The lens configuration is com-

plex, composed of one main lensing gal-axy plus a plausible galaxy cluster at red-shift between 0.6 and 0.8 and anotherpossible group at z L 0.7. Multi-ObjectSpectroscopy is needed in order to con-firm our cluster candidate(s) and deriveits (their) redshift and velocity dispersion.In addition, weak lensing (shear) analy-sis of background galaxies will be usefulto map the overall lensing potential in-volved in this complex system.

References

Aragón-Salamanca, A., Baugh, C.M.,Kauffmann, G., 1998, preprint astro-ph/9801277.

Bade, N., Fink, H.H., Engels, D., et al., 1995,A&AS, 110, 469.

Bade, N., Siebert, J., Lopez, S., et al., 1997,A&A, 317, L13.

Bertin, E., Arnouts, S., 1996, A&AS, 117, 393.Courbin, F., Lidman, C., Magain, P., 1998a,

A&A, 330, 57.Courbin, F., Lidman, C., Frye, B., 1998b, ApJL,

in press (astro-ph/9802156).Hagen, H.-J., Groote, D., Engels, D., Reimers,

D., 1995, A&AS, 111, 195.Kodama, T., Arimoto, N., Barger, A.J., et al.,

1998, preprint astro-ph/9802245.Koo, D.C., Vogt, N.P., Phillips, A.C., et al.,

1996, ApJ, 469, 535.Magain, P., Courbin, F., Sohy, S., 1998, ApJ,

494, 452.Magain, P., Courbin, F., Sohy, S., 1997, The

Messenger, 88, 28.Moorwood, A., Cuby, J.G., Lidman, C., 1998,

The Messenger, 91, 9.Moustakas, L.A., Davis, M., Graham, J.R., et

al., 1997, ApJ, 475, 445.Remy, M., Claeskens, J.F., Surdej, S., et al.,

1998, New Astronomy, in press.

Figure 3: Composite image of a 2 ′ field around RX J0911.4+0551. The frame has been obtained by combining the ALFOSC I and the SOFI J andK-band data. North is up and East is to the left. Note the group of red galaxies with similar colours, about 38 ″ SW of the quadruple lens (circle) andthe group of redder galaxies 10 ″ SW of the lens (cross).

33

O T H E R R E P O R T S F R O M O B S E R V E R S

Astrometry of Comet 46P/Wirtanen at ESO:Preparation of ESA’s ROSETTA MissionJ. SANNER, M. GEFFERT (Sternwarte der Universität Bonn, Germany)H. BÖHNHARDT (European Southern Observatory, Santiago de Chile)A. FIEDLER (Universitätssternwarte München, Germany)

1. A New European Spacecraftto a Comet

1.1 The ROSETTA mission

Comets play an important role in thestudies of the solar system and its origin,because they are believed to containmatter in a primordial form. After thesuccess of the GIOTTO flyby at comet1P/Halley in 1986, ESA plans to send asecond spacecraft named “ROSETTA” toanother comet, 46P/Wirtanen, for a morethorough investigation of a cometary nu-cleus and its physico-chemical nature.After its launch in 2003 and two asteroidflybys during the cruise phase to theprime target, ROSETTA will rendez-vous

with 46P/Wirtanen in 2011 and will orbitthe comet in a distance of 10 to 50 kmuntil at least its subsequent perihelionpassage in 2013. During this orbitingphase it will perform in situ experimentsof the coma, remote sensing of the nu-cleus and, most important, it will alsoplace a lander called “RoLand” with sev-eral scientific experiments on the nucle-us of the comet. The main scientific ob-jectives of the mission are (see also [16]):global characterisation of the nucleus andits dynamic properties, chemical compo-sition, physical properties and interrela-tion of volatiles and refractories in thenucleus.

ROSETTA shall help answering thequestions of the origin of comets, the re-

lationship between cometary and inter-stellar material and its implications withregard to the origin of the Solar System.

The probe is named after the Rosettastone which covers one text in three an-cient scripts (hieroglyphs, demotic andGreek). After its discovery in 1799 it waspossible to decipher the Egyptian hiero-glyphs in 1822. Now the stone is on dis-play in the British Museum in London, UK[13].

1.2 The target comet: 46P/Wirtanen

The comet was discovered on Janu-ary 17, 1948, at Lick Observatory, USA,by Carl A. Wirtanen. With an orbital peri-od of about 5 years, it belongs to the so-called Jupiter family comets, the orbitsof which are subject to repeated closeencounters with the planet Jupiter (thenaltering the orbit parameters severely).The most recent perihelion passage of46P/Wirtanen took place on March 14,1997. The parameters of the current or-bit of the comet from [7] (see also [14])are summarized in Table 1.

During its current revolution, the com-et was recovered in 1995 – with a mag-nitude of about 24.5 in a very crowdedstar field close to the centre of the MilkyWay – at ESO La Silla [1, 2]. The cometwas found to have the smallest nucleusknown so far, i.e. about 600–700 m inradius (measured first by [2] and con-firmed later by HST observations [5]).Recent work based on some of our datareveals a light curve which hints at a ro-tation period of almost 7 hours [3].

The small size of 46P/Wirtanen makesthe mission more difficult: A larger masswould be helpful in keeping the space-craft in orbit around the nucleus and drop-ping the lander onto the surface.

Figure 1: A 600 sec R filter image of comet 46PlWirtanen taken on April 25, 1996, at the Danish1.5-m telescope. North is up and east to the left. The image shows a field of view of 3.3 ′.Wirtanen is marked with an arrow. Note the elongated stellar images due to guiding with respectto the comet.

TABLE 1: Orbital elements of comet Wirtanen.The coordinates are given with respect to equi-nox 2000.0.

Date of perihelion 1997 03 14.14299Distance at perihelion 1.0637469 AUPerihelion Argument 356.34322°Ascending Node 82.20387°Inclination 11.72255°Eccentricity 0.6567490Orbital Period 5.46 years

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2. Astrometry Support for theCometary Mission

For mission-planning purposes, inparticular for an economic planning of theuse of manoeuvre propellant during thecruise phase to the comet, it is importantto know the object’s orbit with a very highaccuracy. The orbit characterisation be-comes particularity difficult because of thenon-gravitational forces. These perturba-tions of the orbit are caused by the out-gasing of the cometary nucleus. There-fore, astrometric positions all along theorbit and over several orbital revolutions

are required for an accurate orbit deter-mination which then can be used for prop-er mission planning of ROSETTA. In thecase of 46P/Wirtanen, it is a difficult taskto obtain such measurements becausethe object is very faint due to its large dis-tance from the Earth and the Sun duringmost of its orbit.

The only possibility to observe distantand faint moving objects and to measuretheir positions accurately and in a suita-ble time (the exposure times must not bearbitrarily long because of the orbitalmotion of the target object!) is given bythe use of CCD imaging. However, this

leads to the problem that due to the smallfield sizes of CCDs, the number of refer-ence stars within the field is too small fora good transformation from the CCD po-sitions to the celestial coordinates.

In the following, we present a recentlydeveloped technique which is tailored forthe determination of very accurate astro-metric positions of faint solar-system ob-jects on small-sized CCD frames. Thepositions of 46P/Wirtanen, which we ob-tained from La Silla observations in 1996,were used to improve the orbit parame-ters of the comet in support of ESA’sROSETTA mission.

Figure 2: Schematic view of the method of datareduction. With Guide Star Catalog 1.2 (blue),the positions of secondary reference stars onimages of the Digitized Sky Survey were com-puted (red). Those reference stars were usedto determine the position of 46P/Wirtanen(green).

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3. The ESO Observations of theComet in 1996

The observations used in our analy-sis were collected at the ESO La Sillaobservatory in Chile in the context of acoordinated campaign for the assess-ment of the nucleus properties and thecoma activity of 46P/Wirtanen in prepa-ration of the ROSETTA mission. TheCCD images were taken in 1996 by var-ious observers (see Table 2) at two dif-ferent telescopes, the 1.54-m Danish tel-escope equipped with DFOSC (2k × 2kCCD with a pixel size of 0.4″) and theESO/MPG 2.2-m telescope equippedwith EFOSC2 (until July 1996 1k × 1kCCD of pixel size 0.32″, thereafter 2k ×2k CCD of pixel size 0.27″). With thesetelescope-instrument combinations, oneobtains images with a field of view of13.7′ (DFOSC) and 5.5′ or 9′ (EFOSC2),respectively. Due to CCD artefacts inDFOSC, only the inner 1500 × 1500 pix-els were useful for our measurements.The images of the comet were exposed

through broadband BVR filters with dif-ferent durations ranging from 30s to 600s(depending on the comet’s brightnessand motion rate). As the telescope wasguided on the target object, the stellarimages were more or less elongated,depending on the exposure times andapparent velocity of the comet.

The main goal of the astrometry partof the programme was to measure thepositions of the comet over the wholeorbit arc from a distance close to the pointwhere ROSETTA will start its sciencemission until almost to perihelion. Theearly observation phase when the com-et was fainter than 20 mag imposed thechallenge to measure the position of avery faint, hardly detectable object on ascary star background. Towards the endof our observing period, its brightnesshad increased to p 14 mag which madeit a more comfortable object, but now alsowith a much higher motion rate since itwas closer to the Earth and the Sun.

From the several hundred frames ofthe comet obtained in 1996 we selected

a total of 79 images (all taken throughBessell R filter) for the astrometric meas-urements. An example image from the firstrun in April 1996 is shown in Figure 1.

4. The Astrometric Data Reduction

Before the astrometric measurementswere performed, all images were biassubtracted and flat-fielded. Due to thesmall fields of the images, classical ref-erence stars from catalogues like theGuide Star Catalog (GSC) [6], PPM StarCatalogue [10, 11], etc. do not cover thesky sufficiently dense to be used directlyfor the astrometric processing of theframes. In addition, most of them weresaturated on the CCD images due to therelatively long exposure times used fordepicting the comet. Therefore, we de-veloped a concept for the determinationof the positions of the comet by the useof secondary reference stars determinedfrom rectangular positions of stars on theDigitized Sky Survey (DSS) [9]: for eachCCD frame, we derived positions of 10to 15 secondary reference stars (coveredboth by the CCD image and DSS) withrespect to about 30 nearby GSC stars.

For the determination of the rectangu-lar pixel coordinates of the objects on theCCD frames and the DSS we used theimexamine routine of the IRAF softwarepackage. Earlier tests of this routine hadshown that a positional accuracy ofabout 0.1 to 0.2 pixel can be achieved[4]. This value corresponds to a position-al uncertainty of less than 0.1″ (corre-sponding to about 300 km at a distanceof 5 AU which is approximately Wirtanen’sdistance during the first measurements),which provides a sufficient accuracy for theastrometry of comets. This uncertaintydoes not play any role for the 2011rendez-vous with ROSETTA, because thenon-gravitational forces do not allow tomake an orbit prediction of the comet tothis level of accuracy over several revo-lutions (and the comet will pass periheliontwice before ROSETTA will arrive).

The improved version 1.2 of the GSC[15] was taken for the reduction. Sincethe GSC does not contain proper motionsand the epochs of the DSS and GSC dif-fer, we omitted all stars showing devia-tions larger than 3σ from the root meansquare (rms) between measurementsand catalogue.

In a first step, the coordinates of thesecondary reference stars on the DSSimages were determined with respect tothe GSC stars with a third order polyno-mial approximation (i.e. 10 plate con-stants). Secondly, the comet’s positionwas computed using the images of thesecondary reference stars on the CCDframes. Figure 2 sketches this method.

5. The Results and Discussion

Figure 3 shows the apparent motionof comet Wirtanen on the sky during thetime of our 1996 observations.

Figure 3: Trajectory of comet 46P/Wirtanen during April to December 1996. Note that the coor-dinates given are topocentric and therefore superimposed by the Earth’s parallax.

TABLE 2: The ESO imaging campaign of comet 46P/Wirtanen. Besides the information on theobserving runs themselves, Wirtanen’s motion rate υ, distances r and ∆ from Sun and Earth,respectively, are given. The values are averaged over the monthly observing periods.

Date ∆ [AU] r[AU] υ [″/h] telescope observer

25.04.96 3.4 3.3 33 1.5-m DK Böhnhardt, Rauer11.–13.05.96 3.1 3.2 28 2.2-m West18.–19.06.96 2.3 3.0 14 1.5-m DK Jorda, Schwehm09.–12.07.96 1.9 2.8 23 2.2-m Peschke18.–23.08.96 1.2 2.5 46 1.5-m DK Thomas, Rauer, Böhnhardt10.–17.09.96 1.5 2.3 33 2.2-m Schulz, Tozzi02.–04.10.96 1.5 2.2 12 1.5-m DK Rauer01.–05.11.96 1.6 1.9 29 1.5-m DK Böhnhardt06.–08.12.96 1.7 1.6 71 1.5-m DK Cremonese, Rembor08.–11.12.96 1.7 1.6 73 2.2-m Rembor, Cremonese

36

The positions obtained [12] revealeda larger than expected offset from thepreviously predicted positions. This indi-cates that the data gathered during earli-er apparitions may be too inaccurate and/or badly sampled to compute a sufficientlyprecise long-term orbit of the comet.

The rms of the deviations betweenDSS measurements and the cataloguepositions was less than 0.2″ correspond-ing to an uncertainty of 0.1″ for the sec-ondary reference stars. We obtained arms of the deviations between catalogueand rectangular coordinates on the CCDframes of better than 0.2″.

For the accuracy of the final positions,we have to consider contributions fromdifferent sources. First of all, the cometappeared as a diffuse object (and not asa point-like star), which leads to problemsin finding the “centre” of the comet. An-other possible error source is the influ-ence of higher-order image distortionsdue to imperfect optics of the telescope/instrument system. However, since in ourimages the comet was located essential-ly in the central region of the frames andsince the secondary reference stars weredistributed evenly over the frame, we thinkthat in our data this effect will be small. Athird problem lies in the motion of the com-et with respect to the star background andthe possible trailing of the comet imagesdue to imperfect telescope guiding, whichlead to elongated images – especially forthe long exposures (up to 600s). More-over, epoch differences of observationsand catalogues in combination with theproper motions of the stars could causesystematic deviations of these positions.All these effects are difficult to evaluate.However, the orbit calculation of the com-et based on our and other positions cangive an estimation of the accuracy of ourastrometry of the comet.

The data were compared with an orbitcalculated by T. Morley (ESA) [8]. He usedall data available from November 1985until December 1996, i.e. three appari-tions of Wirtanen, including our own data.He also took into account the non-gravi-tational forces which he extrapolated fromthe previous apparitions (Non-gravitation-al forces can only be determined a pos-teriori, i.e. long after the correspondingperihelion passage).

From a comparison of our results withthis orbit we obtained “O–C” (observed –calculated) deviations of +0.27″± 0.85″ inα and +0.22″± 0.32″ in δ. The larger de-viations in right ascension are mainly seenin the observations in August and Sep-tember 1996. During this period the com-et had a large motion in right ascension,which caused elongated images and pos-sibly the larger uncertainty of the posi-tions. The deviations in right ascension anddeclination are shown in Figures 4 and 5.

6. Outlook and Summary

46P/Wirtanen will be monitored overthe following years by many observato-

ries. This includes ESO, but it can beexpected that this will be on a smallerlevel than during the 1996 campaign. Theorbit will be continuously improved withnew data as well as the model for the non-gravitational forces. As the ROSETTAprobe will follow a flight path which lets itcatch up slowly with the comet, theground-based observations should al-ready lead to an ephemeris which is suf-ficiently precise to reach the target withvery slight in-flight corrections of the tra-jectory. By that time, also the ESO sup-port can be expected to be on a muchhigher level again. And in the final phase

of the approach, an on-board camera willtake additional images of the comet for afine-tuning of the manoeuvres.

Our work plays a significant role forthe project for two reasons: Firstly, CCDimaging gave the chance to observe Wir-tanen in the remote part of the orbit whichincreased the understanding of the orbititself and the non-gravitational forces, andon the other hand, our method to use theDSS as a coupler between the coarsereference catalogues and the CCD fieldsallows astrometric work on small fieldsof any part of the sky. Of course, themethod is not sufficient for high-precision

Figure 4: Plot of the O–C values in right ascension. The errors are plotted with respect to thetime of observation, given in days of the year 1996. Note the high scatter of the values especial-ly around 250 d (August/September).

Figure 5: Plot of the O–C values in declination. It seems that there is a systematic trend of theO–C values with time. Such effects can be due to an imperfect modelling of the perturbingnon-gravitational forces.

37

astrometry (e.g. proper-motion studies),but it can be very well used for CCD as-trometry of faint solar-system bodies.

References

[1] Böhnhardt H., West R.M., Babion J.,Rauer H., Mottola S., Nathues A., 1996,IAUC 6392, 3.

[2] Böhnhardt H., Babion J., West R.M.,1997, A&A 320, 642.

[3] Böhnhardt H., Fiedler A., Geffert M.,Sanner J., 1997, The ROSETTA/ISO Tar-get Comets Imaging Campaign, Final Re-port of an ESA Study Project.

[4] Geffert M., Reif K., Domgörgen H., BraunJ.M., 1994, AG Abstr. Ser. 10, 125.

[5] Lamy P., 1996, IAUC 6478.[6] Lasker, B.M., Jenkner, H., Russell, J.L.,

1987, The guide star catalog, Space Tele-scope Science Institute.

[7] Marsden B.G., 1996, The Minor PlanetCirculars 27080, eds. B. Marsden, G.V.Williams, S. Nakano.

[8] Morley T., 1997, private communication.[9] Postman M., 1996, Technical Report,

Space Telescope Science Institute, Bal-timore.

[10] Röser S., Bastian U., 1991, PPM StarCatalogue North, Akademischer Verlag.

[11] Röser S., Bastian U., 1993, PPM StarCatalogue South, Akademischer Verlag.

[12] Sanner J., Hainaut O.R., Böhnhardt H.,Rauer H., West R.M., Jorda L., SchwehmG., Thomas N., Schulz R., Tozzi G.-P.,

Cremonese G., Rembor K., 1997, The Mi-nor Planet Circulars 30125, eds. B.Marsden, G.V. Williams, S. Nakano; alsoavailable on-line at http://www.astro.uni-bonn.de/~jsanner/mpc30125.html

[13] ht tp: / /www.br i t ish-museum.ac.uk/highligh.html

[14] http://nssdc.gsfc.nasa.gov/planetary/factsheet/cometfact.html

[15] http://www-gsss.stsci.edu/gsc/gsc12/description.html

[16] http:/www.estec.esa.nl/spdwww/rosetta/html2/toc.html

J. Sannerjsanner@astro.uni-bonn.de

NTT Archives: the Lyman α Profile of the RadioGalaxy 1243+036 RevisitedL. BINETTE 1, B. JOGUET 2, J.C.L. WANG 3 and G. MAGRIS C.4

1Instituto de Astronomía, UNAM, México, DF, México2European Southern Observatory, Santiago, Chile3Astronomy Department, University of Maryland, USA4Centro de Investigaciones de Astronomía, Mérida, Venezuela

Abstract

All observations of very high redshiftradio galaxies attest to a highly complexinteraction between large-scale astro-

physical processes as violent and diverseas that of nuclear activity and of cosmo-gonic star formation. Lyα is seen in emis-sion over scales exceeding galactic siz-es and its resonant nature leads by itself

to a wide range of phenomena such asabsorption lines due to intervening HI gaslayers of very small columns, or en-hanced dust extinction due to the mani-fold increase in path length traversedbefore escape. The resonant nature ofLyα can also manifest itself in emissionthrough the process of Fermi accelera-tion across a shock discontinuity whichleads to a large blueshift of the line pho-tons. We propose that such a process isat work in the radio galaxy 1243+036 (z= 3.6) and can account for the three nar-row emission peaks present on the blueside of the profile. The ultimate source ofthe photons present in those peaks like-ly consists of a jet-induced starburst of M5 107 M0 situated at the position of theradio jet bend. Our investigations illus-trate one possible use of the user friend-ly archival database developed by ESO.

1. General Context

Lyman α is the strongest emission lineobserved in High-Redshift Radio Galax-ies (HZRG). Although the brightness ofthe line reaches a maximum towards thenucleus, most of the emission is spatial-

Figure 1: Velocity shifts of the absorbers rela-tive to line centre as measured by van Ojik etal. (1997). Distinct symbols are used to distin-guish different objects. For instance, all thefour absorbers of 0828+193 are representedby solid squares. Negative and positive ejec-tion velocities are of comparable likelihood.The figure does not contain the absorption dipsreported in 1243+036.

38

ly resolved with the fainter emission ex-tending up to radii 40–130 kpc. The workof van Ojik et al. (1997) shows that thefull width at half-maximum of the integrat-ed Lyα profile is in the range of 700–1600km/s. One striking feature discovered byvan Ojik et al. is that out of 18 intermedi-ate-resolution (Q 3 Å) spectra of HZRG,fully 60% of the objects showed deepabsorption troughs superposed to the Lyαemission profile. The H I absorption col-umn density of the dominant absorber isin the range of 1018–1020 cm–2. In somecases, more than one absorber is pres-ent but with much smaller columns(1014–1016 cm–2). An important conclu-sion reached was that the absorbers werepart of the local environment of the par-ent radio galaxy. The fate and nature ofthe absorbers are still a matter of debate.If one converts into ejection velocities theabsorption trough positions relative to theemission line centre, the smaller columnsshow some tendency towards higher ve-locity shifts as shown in Figure 1. Glo-bally, the sign of the velocity shifts is ran-domly distributed without any strong pref-erence towards either ejection (blueshift)or infall (redshift).

2. The Asymmetric Ly α Profileof 1243+036

The study of van Ojik et al. (1997) re-veals that the underlying Lyα emissionprofiles within their 18 objects sample areremarkably gaussian and symmetriconce allowance is made for the presenceof the absorption troughs (fitted withVoigt profiles). In this respect, 1243+036stands as a noteworthy exception with anasymmetric profile due to a significantexcess of flux on the blue side. Super-posed on this blue excess are narrowfeatures which van Ojik et al. (1996) in-terpreted as four absorption dips. Inter-estingly, these all arise on the blue side,which is uncommon. The Lyα profile of1243+036 is displayed in the top panelof Figure 2. Our proposed and variantinterpretation is that the blue asymmetryconsists merely of three narrow emissionpeaks with little if any absorption at all.This possibility is best illustrated by thedotted blue line of Figure 2 which is thedifference between the blue half and thesmoothed and folded red half of the Lyαprofile. It thus becomes apparent that thenarrow features which stand out most sig-nificantly above noise consist of net emis-sion.

3. Fermi Accelerationand the Equidistant Peaks

A study by Neufeld and McKee (1988)of the transfer of resonant Lyα across ashock discontinuity has shown how therepeated scattering of resonant Lyα pho-tons across the shock front can lead to asystematic blueshift of the line. Theblueshift can greatly exceed the shockvelocity Vs if the H I column density on

either side of the shock is very large, thusproviding a new and interesting explana-tion for the blue asymmetric profiles ob-served in a few radio galaxies.

We have further developed the Neu-feld and McKee (1988) model by ex-tending its validity to the regime of small-er columns in which individual emissionpeaks become identifiable (see Binette,Joguet and Wang, 1998). The close cor-respondence between the model as rep-resented by the red line in Figure 2 andthe emission features is certainly encour-aging. Unlike absorption features whichappear at random velocities, the threeemission peaks occur only in the bluewing, as the Fermi acceleration processwould predict. In fact, each successiveemission peak corresponds to the in-cremental blueshift resulting from twoscatters – back and forth – across theshock discontinuity, with each across-shock scattering giving a blueshift ofVs/2. Multiple scatters and some diffu-sion in frequency still takes place withinthe H I columns on either side of theshock front after each shock crossing.However, the velocity shift incurred bythis frequency diffusion is very small

compared to the huge blueshift obtainedin just a single shock front crossing.Thus, the gas velocity discontinuityacross the shock front provides the mostefficient escape route for resonant Lyαphotons, cutting down the millions of ‘lo-cal’ scatterings otherwise necessary instatic media for escape far in the damp-ing wings to a comparatively smallnumber of scatters (across the shockfront and within the H I columns aftereach shock crossing).

In our model, the separation betweensuccessive peaks gives the shock veloc-ity Vs and must therefore be equal, as isobserved. Our fit gives directly a Vs P300 km/s. The bulk (or the maximum) ofthe Lyα flux emerges at a velocity posi-tion proportional to (NHI Vs)dA. Larger col-umns necessitate more across-shockscatters before escape and so result inLyα emerging in peaks of higher order,farther to the blue. The model shown hereimplies an H I column for each of the twoscattering layers of NHI = 1.3 1021 cm–2.One layer is associated with the preshockgas ahead of the shock and the other isassociated with the recombined gas shellin the trailing postshock gas.

Figure 2: The top panel shows the Lyα profile of 1243+036. Originally taken by van Ojik et al.(1996), the spectrum was retrieved from the ESO archives (http://arch-http.hq.eso.org) andre-reduced by one of us (BJ). Extraction along the long slit was performed using a 7 ″ windowcentred on the radio bend rather than on the nucleus (2 ″ away). The narrow blueshifted fea-tures shown in the bottom panel (blue dotted line) were isolated by subtracting the smoothedand folded red side of the profile. The top abscissa is the observed wavelength scale while thebottom abscissa represents velocity shifts with respect to λ0, the wavelength we attribute tosystemic velocity. The red line is a model based on Fermi acceleration across a shock disconti-nuity moving at 300 km/s. The model was convolved by the instrumental profile which is depict-ed in green.

39

4. A Powerful Jet InducedStarburst in 1243+036?

Using a different slit orientation, VanOjik et al. (1996) report that the blue ex-cess Lyα flux is displaced spatially fromthe nucleus and coincides with the radiojet bend seen in their radio maps 2″south-east of the nucleus. Such a radiobend confirms the existence of a shockwhile its spatial association with Lyα onlyadds to the plausibility of the Fermi ac-celeration model. But what is the ultimatesource of the Lyα photons which areblueshifted across the shock front? Itcannot be the shock itself as this wouldimply absurdly high densities to accountfor the observed Lyα luminosity (p 1043.4

erg/s). It cannot be nuclear photoionisa-tion since the existence of two neutral gasmirrors bracketing the accelerated Lyαphotons is essential to the Fermi accel-

eration process; nuclear photoionisationwould prevent the trailing H I mirror fromexisting. The most plausible explana-tion remaining is that of a colossaljet-induced starburst, similar in nature tothat envisaged by Rees (1989). Moreo-ver, the non-detection of C IV emissionin 1243+036 argues against nuclear pho-toionisation or shock excitation and fa-vours the starburst picture. Interestingly,the ubiquitous C IV line has also beenreported missing in 3C326.1, another ra-dio galaxy with asymmetric Lyα to whichNeufeld and McKee (1988) applied theirnovel Fermi acceleration model. It maybe that blue asymmetric Lyα profiles area sign of extranuclear starbursts. Adopt-ing a Salpeter initial mass function ofslope 1.35 which extends from 0.1 to 125M0, we derive a luminosity for the hotstars of 1.3 1054 ionising photons/s fromthe observed Lyα luminosity. Assuming

an instantaneous burst of star formationwith this initial mass function gives a massof newly formed stars of M 5 107 M0 (Bru-zual and Chariot, 1996).

References

Binette, L., Joguet, B., Wang, J.C.L., 1998, ApJin press.

Bruzual A., G. and Charlot, S., 1996, in A DataBase for Galaxy Evolution Modeling, eds.C. Leitherer et al., PASP, 108, 996.

Neufeld, D.A., McKee, C.F., 1988, ApJ 331,L87.

Rees, M.J., 1989, MNRAS 239, 1P.van Ojik, R., Röttgering, H.J.A., Carilli, C.L.,

Miley, G.K., Bremer, M.N., Macchetto, F.,1996, A&A 313, 25.

van Ojik, R., Röttgering, H.J.A., Miley, G.K.,Hunstead, R. W., 1997, A&A 317, 358.

L. Binettebinette @astroscu.unam.mx

Photos from Science Writers’ SymposiumOn the occasion of the VLT UT1

First-Light Event, a Science Writ-ers’ Symposium took place onMonday, April 27, and Tuesday,April 28, 1998, at the ESO Head-quarters (Garching, Germany)with a complete briefing for mediarepresentatives about the VLTProject (technology, science) andits continuation after the UT1 FirstLight. The presentations weremostly made by ESO technical andscientific staff. About 40 media rep-resentatives participated, from allESO member countries and be-yond.

The ESO Director General, Prof. Ric-cardo Giacconi, introduces the VLT andits many scientific and organisationalaspects. E

Massimo Tarenghi during the teleconference with Paranal. On theother side, at Paranal, Jason Spyromilio and Peter Gray.

The participants enjoy the teleconference with Paranal.

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A N N O U N C E M E N T S

Joint Committee Between ESO and the Government of Chilefor the Development of Astronomy in Chile

In accordance with Article Nine of theinterpretative, supplementary andamending agreement to the “Conven-tion between the Government of Chileand the European Organisation for As-tronomical Research in the SouthernHemisphere for the Establishment of anAstronomical Observatory in Chile”, aJoint Committee has been constituted,on 13 March 1998, to co-operate direct-ly in programmes for training young sci-entists, for engineers and technologists,and for equipment in general. The found-ing document was officially signed bythe Minister of Foreign Affairs, His Ex-cellency Mr. José Miguel Insulza S., andthe ESO Director General, Prof. R. Gi-acconi.

The membership of this Committeeconsists of three representatives of theGovernment of Chile, the Director of“Política Especial”, Ambassador R. Gon-zález, the Chairman of the PresidentialCommission for scientific matters, Dr. C.Teitelboim, and the Australian AstronomerDr. K. Freeman, and three representa-tives of ESO, the Associate Director forScience, Dr. J. Bergeron, the Director ofthe Paranal Observatory, Dr. M. Taren-ghi, and the ESO Representative in Chile,D. Hofstadt.

To foster scientific and technical co-op-eration between ESO and Chile, ESO willprovide and administrate funds allocat-ed for the development of astronomy andrelated technologies in Chile. The JointCommittee has the responsibility to de-fine the framework of the co-operation,and to evaluate and select the pro-grammes which will be financed by thesefunds.

Prior to the first meeting of the JointCommittee, extensive consultation tookplace between the Chilean astronomersand Dr. K. Freeman. The discussionsduring the meeting were very positive,and unanimous decisions were easilyreached. On 13 March 1998, the JointCommittee agreed to make an announce-ment of opportunities for the six pro-grammes summarised below:

• Creation of new astronomical re-search groups. To help Chilean Aca-demic Institutions in the creation of anastronomical group, ESO will share withthe selected Academic Institution thecosts of hiring a full professor for a two-year period and two associate profes-sors for a one-year period. After thoseterms have expired, the Academic Insti-tution will take over the established pro-gramme.

• Complementary funding for post-doctoral Astronomy programmes. Thegoal of this programme is to make post-doctoral positions at Chilean AcademicInstitutions competitive at the internation-al level.

• Strengthening of already estab-lished astronomical research groups.To this end, ESO will finance two newposts for full or associate professors fora three-year period. This term may beextended to a five-year period. After thoseterms have expired, the hosting Aca-

demic Institutions will commit themselvesto maintain these new positions.

• Training of professors for theteaching of astronomy in highschools. Special attention will be givento programmes which are already spon-sored, and ESO will share their funding.

• Research infrastructure. The goalof this programme is to strengthen theresearch capacities of academic institu-tions.

• Development of systems and in-struments. Chilean engineers and tech-nicians will be invited to participate,through public tenders, in the develop-ment of systems and instruments for theVLT telescope units.

The total level of funding available in1998 for this ESO-Chile co-operation pro-gramme is DM 660,000. Additional pro-grammes by ESO (for DM 340,000 in1998) include social help to local com-munities, education programmes in highschools and university scholarships.

ESO Imaging Survey: Update on EIS-deepand the Hubble Deep Field South

L. DA COSTA and A. RENZINI, ESO

The second part of EIS (deep), as orig-inally recommended by the EIS WorkingGroup, envisioned the observation of a15 ×15 arcmin region centred on the HST

Hubble Deep Field South (HDF-S), in sixpassbands (the EIS proposals for Peri-ods 59, 60, and 61 can be found at http://www.eso.org/research/sci-prog/eis/eis_

obs.html). The programme was split be-tween Periods 61 and 62, and 7 SUSI2and 6 SOFI nights in Period 61 have al-ready been allocated. However, with the

41

ESO Fellowship Programme 1999The European Southern Observatory (ESO) awards up to six postdoctoral fellowships tenable at the ESO Headquarters, located in

Garching near Munich, and up to six postdoctoral fellowships tenable at ESO’s Astronomy Centre in Santiago, Chile. The ESO fellowshipprogramme offers a unique opportunity to learn and to participate in the process of observational astronomy while pursuing a researchprogramme with state-of-the-art facilities.

ESO facilities include the Very Large Telescope (VLT) Observatory on Cerro Paranal, the La Silla Observatory and the astronomicalcentres in Garching and Santiago. At La Silla, ESO operates eight optical telescopes with apertures in the range from 0.9 m to 3.6 m, the 15-m SEST millimetre radio telescope, and smaller instruments. The VLT consists of four 8-m diameter telescopes. First light for the firsttelescope is expected late May 1998. Both the ESO Headquarters and the Astronomy Centre in Santiago offer extensive computing facilities,libraries and other infrastructure for research support. The Space Telescope European Coordinating Facility (ST-ECF), located in the ESOHeadquarters building, offers the opportunity for collaborations. In the Munich area, several Max-Planck Institutes and the University Observ-atory have major programmes in astronomy and astrophysics and provide further opportunities for joint programmes. In Chile, astronomersfrom the rapidly expanding Chilean astronomical community collaborate with ESO colleagues in a growing partnership between ESO and thehost country’s academic community. The main areas of activity at the Headquarters and in Chile are:

• research in observational and theoretical astrophysics;• constructing and managing the VLT;• developing the interferometer and adaptive optics for the VLT;• operating the Paranal and La Silla observatories;• development of instruments for the VLT and La Silla telescopes;• calibration, analysis, management and archiving of data from ESO telescopes;• fostering co-operation in astronomy and astrophysics within Europe and Chile.

In addition to personal research, fellows spend a fraction of their time on the support or development activities mentioned above:In Garching, fellows are assigned for 25% of their time to an instrumentation group, a user support group or a telescope-operation team

in Chile. The fellowships are granted for one year with the expectation of a renewal for a second year and exceptionally a third year.In Chile, the fellowships are granted for one year with the expectation of a renewal for a second and third year. During the first two years,

the fellows are assigned to a Paranal operations group or a La Silla telescope team. They support the astronomers at a level of 50% of theirtime, with 80 nights per year at either the Paranal or La Silla observatory and 35 days per year at the Santiago Office. During the third year,two options are provided. The fellows may be hosted by a Chilean institution and will thus be eligible to propose for Chilean observing timeon all telescopes in Chile; they will not have any functional activitiy. The second option is to spend the third year in Garching where the fellowswill then spend 25% of their time on the support of functional activities.

The basic monthly salary will be not less than DM 4853 to which is added an expatriation allowance of 9–12% in Garching, if applicable,and up to 40% in Chile. The remuneration in Chile will be adjusted according to the cost of living differential between Santiago de Chile andthe lead town Munich. The fellow will also have an annual travel budget, for scientific meetings, collaborations and observing trips, ofapproximately DM 12,000.

Fellowships begin between April and October of the year in which they are awarded. Selected fellows can join ESO only after havingcompleted their doctorate.

Applications must be made on the ESO Fellowship Application Form. The form is available either at URL http://www.hq.eso.org/gen-fac/adm/pers/vacant/fellow.html or from the address below. The applicant should arrange for three letters of recommendation from personsfamiliar with his/her scientific work to be sent directly to ESO. Applications and the three letters must reach ESO by October 15, 1998 (but notearlier than June 1998).

Completed applications should be addressed to:

European Southern ObservatoryFellowship ProgrammeKarl-Schwarzschild-Str. 2D-85748 Garching bei München, Germany

Tel.: 0049-89-32006-438 or -219 — Fax: 0049-89-32006-497e-mail: ksteiner@eso.org

secured for spectroscopic studies withFORS1 and ISAAC, for which teams inthe community may wish to apply to theOPC. Note that HDF-S may also be ob-served with the VLT first Unit Telescopeas part of the VLT Science Verification(see article by Leibundgut, de Marchi andRenzini in this issue).

2. The remaining deep imaging ob-servations will be conducted in the di-rection of the region with the lowest H Icolumn density in the Southern Hemi-sphere (α = 03h 32m 28s = −27° 48′ 30″),equivalent to the well-known Lockmanhole in the North. The field contains veryfew stars, hence it is ideally suited forvery deep optical imaging. It has alsobeen chosen for a very deep AXAF ex-posure (field size 15 × 15 arcmin). Thefield will be covered by four contiguoustiles (10 × 10 arcmin) with both SUSI2and SOFI, with the same filters and depthas for the HDF-S field. Besides J and

Ks imaging, H-band observations arealso proposed for this field. This willmake the data coverage of this fieldequivalent to that of the HDF-S fieldwhere the H-band observations will becarried out and made public by CTIO.

The recommended limiting magni-tudes at 5σ remain the same as in theproposal for Period 61, while the ‘g’-bandimaging has been replaced by B and Vobservations since an optimal ‘g’-bandfilter is not yet available. For the opticalpassbands the targeted limiting magni-tude is p 26 mag in all filters. In the infra-red the observations are expected toreach J p 23.5, H p 22.5 and Ks p 21.5,except in the WFPC2 field where the WGhas recommended that the SOFI obser-vations should reach p 0.5 magnitudedeeper than in the other fields.

More information on EIS-deep can befound at “http://www.eso.org/eis”

final selection of the HDF-S by ST ScI(α = 22h32m56s, δ = 60°33′02″) it becameclear that the selected field is not idealfor deep imaging as it contains severalrelatively bright stars. Taking this intoaccount, the EIS Working Group in itsmeeting of January 21–22, 1998 decid-ed to recommend a different field cover-age for EIS-deep. The WG now propos-es EIS-deep to cover the minimum arearequired to include all HDF-S fields(WFPC2, NICMOS, STIS) and use theremaining observing time to cover a newfield at high galactic latitude. In accord-ance to the reviewed strategy, the follow-ing observations are now planned, pend-ing the endorsement of the OPC for thosein Period 62:

1. The observations of the HDF-S willcover three adjacent SOFI/SUSI2 fields(5 × 5 arcmin each) which will include theWFPC2, NICMOS and STIS fields. In thisway adequate target selection can be

42

FIRST ANNOUNCEMENT

ESO Conference onChemical Evolution from Zero to High Redshift

ESO Headquarters, Garching, Germany

October 14–16, 1998

The topic of the conference is the determination and interpretation of chemical abundances and evolution from stars, interstellar mediumand local group galaxies at zero redshift to distant galaxies, clusters of galaxies and inter-galactic medium at high redshift. Whilst problemsundoubtedly remain in the determination of stellar and nebular abundances in the nearby Milky Way, results are beginning to converge.

The observational and interpretative tools are starting to be mature enough that they can be applied with some confidence to extra-galactic systems and integrated populations at increasingly high redshift.

Ultimately the tools should be applicable to determination of the chemistry and enrichment of young galaxies at large look-back times.The broad aim of the conference is to assess the interplay between methods of measuring chemical abundances with the astrophysical

models of galaxy evolution. About half of the conference will be devoted to consideration of abundances and the factors that regulate themin nearby well-studied systems of the Milky Way and Local Group Galaxies. The remainder will concentrate on more distant systems wherethe abundance data is more slender and the tools under refinement. In addition there will be sessions on forthcoming and future instrumen-tation applicable to abundance determinations across the whole electromagnetic spectrum. The format for the meeting is invited talks, withcontributed papers as talks or posters and some discussion sessions.

There will be five main facets to the conference. The invited speakers are indicated.

• Milky Way stellar and ISM abundance patterns and their models(Gustafsson, Lennon, Peimbert, McWilliam, Meyer and Matteucci)

• Abundances in nearby galaxies and clusters: observations(Pagel, Skillman, Garnett, Worthey and Renzini)

• Evolution of abundances (e.g. effect of dynamics, mergers, supernovae)(Thielemann, Edmunds, Haehnelt and Kauffmann)

• Abundances in the distant Universe (QSO absorption lines and starburst galaxies) and primordial abundances(Pettini, Songaila, Combes,Leitherer and Tytler)

• New windows on abundance determinations in the UV, optical-IR, X-ray and radio(Jenkins, D’Odorico, Kahn and Thatte)

Conference summary by S. White

Scientific Organising Committee:F. Combes, D. Garnett, G. Kauffmann, C. Leitherer, D. Lennon, J. Mathis [Chair], M. Pettini, M. Rosa, P. Shaver, E. Terlevich

Local Organising Committee:G. Contardo, J. Walsh, C. Stoffer

Registration has already begun and the deadline for registration is 1 August 1998.

More details and a registration form can be found at:http://www.eso.org/gen-fac/meetings/chemev98/or contact: chemev98@eso.org for further information.

The Astronomical Almanac to Be RevisedThe U.S. Naval Observatory and the Royal Greenwich Observatory are currently conducting a thorough review of the content and format

of the Astronomical Almanac.In order to assess the needs of the users, a survey is being conducted by the two offices and users can make their needs known in detail

by accessing the site http://www.ast.cam.ac.uk/nao/survey.html or writing to Dr. Alan D. Fiala adf@newcomb.usno.navy.mil.The survey will close on 1 August 1998.

List of Scientific Preprints(March–May 1998)

1263. Contributions of the ESO Data Management and OperationsDivision to the SPIE Workshop “Observatory Operations to Op-timize Scientific Return”. 20–21 March 1998.

1264. P.A. Mazzali et al.: Nebular Velocities in Type Ia Supernovaeand their Relationship to Light Curves.

1265. O.R. Hainaut et al.: Early Recovery of Comet 55P/Temple-Tuttle. A&A.

1266. J.C. Vega Beltrán et al.: Mixed Early- and Late-Type Propertiesin the Bar of NGC 6221: Evidence for Evolution Along the HubbleSequence. A&A.

1267. M. Turatto et al.: The Peculiar Type II Supernova 1997 D: A Casefor a Very Low 56Ni Mass.

1268. F. Bresolin et al.: An HST Study of Extragalactic OB Associa-tions. The Astronomical Journal.

1269. F. Comerón et al.: ISO Observations of Candidate Young BrownDwarfs. A&A.

1270. D.R. Silva and G.D. Bothun: The Ages of Disturbed Field El-liptical Galaxies: I. Global Properties. The Astronomical Jour-nal.

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PRELIMINARY ANNOUNCEMENT

ESO Workshop on Minor Bodies in the Outer Solar System

ESO Headquarters, Garching, Germany

November 2–5, 1998

A four-day ESO Workshop on Minor Bodies in the Outer Solar System (ESO MBOSS-98), their orbital and physical characteristics, as wellas their origins and inter-relationships will be held at a time when several new observational facilities, including the ESO Very Large Tele-scope (VLT), are about to enter into operation. With larger collecting areas and equipped with a host of advanced instruments, they have thepotential of revolutionising observational studies of these faint objects. An overview of this active research field at this time will thereforeprovide an important contribution to the efficient planning of these investigations.

This is a hot subject in current solar-system studies. There is an image emerging of interconnections between Jovian Trojans, theCentaurs, the newly found classes of TNO’s, comet nuclei, interplanetary dust and the icy moons of outer planets, including Pluto itself. TheESO Workshop will allow observers and theoreticians to get together and to discuss plans for future studies in this rapidly evolving field. Theemphasis will be on establishing a comprehensive, overall picture which attempts to describe the formation, evolution and interaction ofthese components.

The meeting will be held in the ESO main auditorium, and the number of participants is therefore limited to a maximum of approximately120.

The main topics of the Workshop will be the following:

• Inventory of Minor Bodies in Outer Solar System (overview)

• Outer Solar System reservoirs (Outer Main Belt and Trojans; Centaurs and Interplanetary Rings; TNO’s and Edgeworth-Kuiper Belt; Trans-Neptunian Disk and Oort Cloud)

• Orbital dynamics and evolution (High-precision orbital determinations; Resonance trapping; Similarity and diversity oforbital types; Pathways between the reservoirs)

• Physical properties (Size, shape and rotation; Composition and atmospheres)

• Physical interrelationships (Transitional asteroid/comet cases; Interplanetary dust)

• Origin and physical evolution (Theories of planetary formation; Collisional history; Growth and physical evolution)

• Future lines of research (Research possibilities with new generation of very large telescopes; Spacecraft missions;Innovative techniques; Collaboration/coordination)

Scientific Organising Committee:

Rudi Albrecht (ST/ECF, Garching, Germany); Mark Bailey (Armagh Observatory, N. Ireland, UK); Hermann Boehnhardt (ESO, Santiago,Chile); Martin Duncan (Queen’s University, Kingston, Ontario, Canada); Julio A. Fernandez (Universidad de la Republica, Montevideo,Uruguay); Alan Fitzsimmons (Queen’s University, Belfast, N. Ireland, UK; SOC Chair); David Jewitt (Institute of Astronomy, Honolulu, Hawaii,USA); Hans Rickman (Astronomiska Observatoriet, Uppsala, Sweden); Alan Stern (South-West Research Institute, Austin, Texas, USA);Jun-ichi Watanabe (National Observatory, Tokyo, Japan); Richard West (ESO, Garching, Germany; LOC Chair)

More details and a registration form can be found at: http://www.eso.org/gen-fac/meetings/mboss98/or contact: rwest@eso.org for more information or one of the SOC members.

1271. P.A. Woudt et al.: Multiwavelength Observations of a Seyfert 1Galaxy Detected in ACO 3627. A&A.

1272. E. Tolstoy et al.: WFPC2 Observations of Leo A: A PredominantlyYoung Galaxy within the Local Group. The Astronomical Journal.

1273. Th. Rivinius et al.: Stellar and Circumstellar Activity of the Be StarµCen. II. Multiperiodic Low-Order Line-Profile Variability. A&A.

PERSONNEL MOVEMENTSInternational Staff (1 April – 30 June 1998)

ARRIVALS

EUROPE

MØLLER, Palle (DK), User Support AstronomerTOLSTOY, Eline (NL),Fellow Garching

CHILE

FRANÇOIS, Patrick (F), AstronomerSTERZIK, Michael (D), Astronomer

DICHIRICO, Canio (I), Temporary transfer to ParanalGIORDANO, Paul (F), Temporary transfer to ParanalDOUBLIER, Vanessa (F), Fellow La SillaPATAT, Ferdinando (I), Fellow La SillaMARCO, Olivier (F), Fellow La SillaVANZI, Leonardo (I), Fellow La SillaSELMAN, Fernando (RCH), Associate

DEPARTURES

EUROPE

HERLIN, Thomas (DK), Software EngineerHESS, Matthias (D), Mechanical EngineerVAN DIJSSELDONK, Anton (NL), Opt. Lab. TechnicianKAPER, Lex (NL), Senior Fellow GarchingBÜTTINGHAUS, Ralf (D), MechanicCRANE, Philippe (USA), Astronomer/Physicist

CHILE

GREDEL, Roland (D), AstronomerKRETSCHMER, Gerhard (D), Mechanical Engineer

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ESO, the European Southern Observato-ry, was created in 1962 to . . . establishand operate an astronomical observatoryin the southern hemisphere, equipped withpowerful instruments, with the aim of fur-thering and organising collaboration in as-tronomy . . . It is supported by eight coun-tries: Belgium, Denmark, France, Germa-ny, Italy, the Netherlands, Sweden andSwitzerland. It operates the La Silla ob-servatory in the Atacama desert, 600 kmnorth of Santiago de Chile, at 2,400 m al-titude, where fourteen optical telescopeswith diameters up to 3.6 m and a 15-m sub-millimetre radio telescope (SEST) are nowin operation. The 3.5-m New TechnologyTelescope (NTT) became operational in1990, and a giant telescope (VLT = VeryLarge Telescope), consisting of four 8-mtelescopes (equivalent aperture = 16 m)is under construction. It is being erectedon Paranal, a 2,600 m high mountain innorthern Chile, approximately 130 kmsouth of Antofagasta. Eight hundred sci-entists make proposals each year for theuse of the telescopes at La Silla. The ESOHeadquarters are located in Garching,near Munich, Germany. It is the scientific,technical and administrative centre of ESOwhere technical development programmesare carried out to provide the La Silla ob-servatory with the most advanced instru-ments. There are also extensive facilitieswhich enable the scientists to analyse theirdata. In Europe ESO employs about 200international Staff members, Fellows andAssociates; at La Silla about 50 and, in ad-dition, 150 local Staff members.

The ESO MESSENGER is published fourtimes a year: normally in March, June, Sep-tember and December. ESO also publish-es Conference Proceedings, Preprints,Technical Notes and other material con-nected to its activities. Press Releases in-form the media about particular events. Forfurther information, contact the ESO Infor-mation Service at the following address:

EUROPEANSOUTHERN OBSERVATORYKarl-Schwarzschild-Str. 2D-85748 Garching bei MünchenGermanyTel. (089) 320 06-0Telex 5-28282-0 eo dTelefax (089) 3202362ips@eso.org (internet)ESO::IPS (decnet)

The ESO Messenger:Editor: Marie-Hélène DemoulinTechnical editor: Kurt Kjär

Printed byDruckbetriebe Lettner KGGeorgenstr. 84D-80799 MünchenGermany

ISSN 0722-6691

ContentsFirst Light ............................................................................................................ 1R. Giacconi: First Light of the VLT Unit Telescope 1 ........................................... 2The Final Steps Before “First Light” .................................................................... 3R.M. West: VLT First Light and the Public .......................................................... 4

OBSERVING WITH THE VLT

B. Leibundgut, G. de Marchi, A. Renzini: Science Verification of theVLT Unit Telescope 1 ..................................................................................... 5

Scientific Evaluation of VLT-UT1 Proposals. Observing Period 63 (April 1 –October 1, 1999) ............................................................................................ 9

P. Quinn, J. Breysacher, D. Silva: First Call for Proposals .................................. 9

TELESCOPES AND INSTRUMENTATION

R.G. Petrov, F. Malbet, A. Richichi, K.-H. Hofmann: AMBER, the Near-Infrared/Red VLTI Focal Instrument ............................................................................ 11

NEWS FROM THE NTT: G. Mathys ......................................................................... 14Ph. Gitton and L. Noethe: Tuning of the NTT Alignment ..................................... 15THE LA SILLA NEWS PAGE

M. Kürster: CES Very Long Camera Installed ..................................................... 18J. Brewer and J. Andersen: Improving Image Quality at the Danish 1.54-m

Telescope ...................................................................................................... 18VLT DATA FLOW OPERATIONS NEWS: D. Silva: The NTT Service Observing

Programme: Period 60. Summary and Lessons Learned ............................. 20A. Moorwood: SOFI Infrared Images of the “NTT Deep Field” ............................ 25

OBSERVATIONS WITH THE UPGRADED NTT

P. Bonifacio and P. Molaro: Upgraded NTT Provides Insights Into CosmicBig Bang ........................................................................................................ 26

R. Neuhäuser, H.-C. Thomas, F.M. Walter: Ground-Based Detection of theIsolated Neutron Star RXJ185635-3754 at V = 25.7 Mag with theUpgraded NTT ............................................................................................... 27

I. Burud, F. Courbin, C. Lidman, G. Meylan, P. Magain, A.O. Jaunsen,J. Hjorth, R. Østensen, M.I. Andersen, J.W. Clasen, R. Stabell,S. Refsdal: RX J0911.4+0551: A Complex Quadruply ImagedGravitationally Lensed QSO .......................................................................... 29

OTHER REPORTS FROM OBSERVERS

J. Sanner, M. Geffert, H. Böhnhardt, A. Fiedler: Astrometry ofComet 46P/Wirtanen at ESO: Preparation of ESA’s ROSETTA Mission ............ 33L. Binette, B. Joguet, J.C.L. Wang, G. Magris C.: NTT Archives: the Lyman α

Profile of the Radio Galaxy 1243+036 Revisited ........................................... 37Photos from Science Writers’ Symposium .......................................................... 39

ANNOUNCEMENTS

Joint Committee Between ESO and the Government of Chile for the Develop-ment of Astronomy in Chile ............................................................................ 40

L. da Costa and A. Renzini: ESO Imaging Survey: Update on EIS-deep and theHubble Deep Field South .................................................................................... 40ESO Fellowship Programme 1999 ...................................................................... 41First Announcement of an “ESO Conference on Chemical Evolution from Zero

to High Redshift” ............................................................................................ 42The Astronomical Almanac to Be Revised .......................................................... 42List of Scientific Preprints (March–May 1998) .................................................... 42Preliminary Announcement of an “ESO Workshop on Minor Bodies in the

Outer Solar System” ...................................................................................... 43Personnel Movements (1 April – 30 June 1998) ................................................. 43

Local Staff (1 April – 30 June 1998)

ARRIVALS

RICHARDSON, Felipe (RCH), Software Engineer DeveloperRODRIGO, Manuel (RCH), Scientific Instruments Operator/ Night AssistantMONTES, Lucía (RCH), Bilingual Secretary

DEPARTURES:

WENDEROTH, Erich (RCH), Scientific Instruments OperatorTIMMERMANN, Gero (RCH), Electronic