The light elements in a helio- and astero- seismic perspectiveobs Vauclair.pdf · The light...
Transcript of The light elements in a helio- and astero- seismic perspectiveobs Vauclair.pdf · The light...
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The light elements in a helio- and astero-seismic perspective
IAU symposium 268, Light elements in the Universe, Geneva, November 9 to 13, 2009
Sylvie Vauclair
Laboratoire d’astrophysique de Toulouse-Tarbes, CNRS, Université de Toulouse, Institut universitaire de France
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1 Mo
20 Mo
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Helium 4 is directly related to asteroseismology as its abundancemodifies stellar structure.-> it may lead to mechanism-> Y may be determined from seismology-> internal helium gradients have seismic signatures
Light elements and seismology
LiBeB and He3 are indirectly related to asteroseismology through the determinations of macroscopic motions (convective zones, internal mixing) which have seismic signatures
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Also Leibacher and Stein 1971, Astrophys Lett 7, 191
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Helioseismology
Special case for the Sun compared to other stars
due to the spatial resolution.
Spatial filter: generalised 2D Fourier transform
Spherical harmonics:
is a Legendre polynomial
is a normalisation factor, so that the integral of
on the sphere is 1.
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* Beginnings : south pole (Grec, Fossat, Pomerantz, 1980)* Observation networks: GONG+ (Doppler), BiSON (integrated light), etc.* Space : SoHO-Solar and Heliospheric Observatory
Helioseismology
* 10 millions of p-modes* Frequencies around 2 to 4 mhz (5min.)* Velocity amplitudes : about 1 cm.s-1 (max:20 cm.s-1)* Relative light variations : 10-7
* Lifetime of modes :a few hours for large l ( ~ 250) and small n ( ~ 1)a few months for small l (~ 0) and large n( ~ 10)
*For l < 180: global modes (lifetime larger than the propagation time around the Sun )
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Bottom convective zone : r/R = .713 .003 (science, 1996)
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Effects of atomic diffusion and turbulence below the convective zone(cf Richard et al. A&A, 1996)
Ys from seismic inversions (from 1)
0.248 +/- 0.02 (Dziembowski et al. 1998 )
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Solar internal rotation
Eff-Darwich et al. 2002Garcia et al. 2008
Shallow tachocline, solid body rotation in most of the Sun…
Gravity waves? Magnetic field? Other? Cf Charbonnel, Talon, Zahn,
Gough et al….
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THE CRISIS!
New solar abundances
Asplund et al 2005
Revised
(here: Serenelli et al. 2009)
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Castro et al 2007
Accretion of
metal poor matter
(Cf. Nordlund 2009)
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Meléndez et al. 2009
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1 Mo
20 Mo
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sun
mu Arae
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Basics of asterosismology(for slowly rotating stars)
« asymptotic theory » (Tassoul 1980) :
Large separations : (n,l) = (n+1, l) – (n,l)
Small separations :
o
échelle diagram
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Negative small separations
Example: HD 52265 (« Corot Star ») Left : Main Sequence ; right : Subgiant
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Asterosismology :ground based and space observations
Same instruments as for the detection of exoplanets
Ground: radial velocity methodsHARPS (La Silla), SOPHIE (OHP), AAT, VLT, Keck, etc…future: SONG
Space: photometric methodsMOST, COROT, KEPLER…
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At least 4 planets-host stars already observed on large periods (8 or 9 consecutive nights)
+ HD52265 (CoRoT star) :
mu Arae, HARPS 2004
iota Hor, HARPS 2006
51 Peg, SOPHIE 2007
94 Cet, HARPS 2007
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1.6Mo , 1.6 Gyrwith diffusion without diffusion
Caracterisation of Ysurf and helium gradients
Frequency fluctuations due to wave partial reflexion in regions of rapid variations of c
Second differences : n n+1 + n-1 – 2 n
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Example: The roAp star HD 60435, Possible helium gradient at r/R = 0.93
(Vauclair et Théado 2004)
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second example (theoretical) :Helium gradients in solar type stars Castro et Vauclair 2006
solid lines: with diffusiondashed lines: without diffusion
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1st ex: mu Arae, HD 160691
43 detected modes , l = 0 to 3Ages from chromospheric index:
6.41 Gyr (Donahue 93)
1.45 Gyr ( Rocha Pinto and Maciel 98)
(Cf. Saffe, Gomez & Chavero 2008)
Yinit determinations
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2nd ex: iota Horologii
8 nights with HARPS, November 2006
25 identified modes
Laymand, Bouchy, Vauclair et al.
Ages (Gyr): 1.47 (D93); 0.43 (RPM98)
Isochrones: 3.6 (1.1 to 6.7) ; (Saffe et al.)
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1.06 Msun
1.20 Msun
1.15 Msun
1.10 Msun
L/L
sun
Ex of model computations:Arae
(Soriano et al. 2009)
YG
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iota Hor ->
<- mu Arae
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M/Mo = 1.25 +/- 0.01
Log g = 4.40 +/- 0.01
Y = 0.255 +/- 0.015
[Fe/H] = 0.16 +/- 0.03
Age = 625 +/- 5 Myr
M/Mo = 1.10+/- 0.01
Log g = 4.215+/- 0.01
Y = 0.30+/- 0.01
[Fe/H] = 0.30 +/- 0.03
Age = 6.34+/- 0.4 Gyr
Note: does not include uncertainties on physics: opacities, EOS, nuclear reactions rates, etc.
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- Crisis for the Sun
-It is just beginning for solar type stars
-Determinations of Y in progress
-Other elements… non standard mixing? (cf Eggenberger)
-Improvements with CoRoT and Kepler.
conclusions