Metallicity and age of selected nearby G-K Giants
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Transcript of Metallicity and age of selected nearby G-K Giants
Metallicity and age of selected nearby G-K Giants
L. Pasquini (ESO)
M. Doellinger (ESO-LMU)
J. Setiawan (MPIA)
A. Hatzes (TLS), A. Weiss (MPA), O. von der Luhe (KIS)
L. da Silva (ON), R. de Medeiros (UFRN)
L. Girardi (INAF-OAP), M.P. di Mauro (INAF-OAR) Setiawan et al. 2003a,b, 2004, 2005, da Silva et al. 2006, Doellinger et al. 2006a,b
Why ‘Selected’ ??
These G and K giants have been selected to be studied for accurateradial velocity measurements, to understand the nature and evolution of RV variations among evolved late-type stars
Many Giants are known to be RV variables, with
• ‘short’ timescales (hours to days) Pulsations ? Solar-type oscillations?
• ‘long’ timescales (hundreds of days) Planets? Inhomogeneities (rotational modulation)?
How frequent are they ? Which amplitude? How do they evolve along the H-R diagram with mass, age etc.. ??
Sample(s)
Stars: G-K giants with accurate HIPPARCOS parallaxes (10%); not known binaries, distributed along the H-R diagram 2 groups: 77 stars from the South, 62 from the North
Southern Observations: FEROS-La Silla, 1999-2003 (ongoing) R=50000; RV ~22 m/sec (Setiawan et al. 2004)
Northern Observations: TLS H-R spectro. 2004-2006 (ongoing) R=67000 RV ~5 m/sec (Döllinger et al. 2006a) (circumpolar objects)
The Sample: H-R diagrams
Southern Sample
Northern SampleSubgiants, RGB stars, Clump Stars, early AGB
RV: Statistics
Northern Stars 11 Binaries (16%)6 Constant (9%)
9 Long Period (15%)
1 Planet confirmed
36 Short Period (60%)
RV~5 m/sec
Southern Stars13 Binaries (17%)21 Constant (27%)
43 Variable (56%)
3 Planets confirmed
8 Activity Modulationor pulsation : Ca II and/or bisector variationswith Period RV~22 m/sec
RV along the H-R diagram
Does RV depends on the absolute stellar magnitude (Southern Sample) ?
Apparent trends are ‘contaminated’ by different physical causes
•BD comp.Planets
Further causes of RV
The apparent trend requires a close scrutiny….
Indications that the most luminous stars show inhomogeneity modulation
Chemical analysis
The well known age-metallicity degeneracy requires determination of [Fe/H] to derive more precise stellar characteristics
FEROS and TLS spectra (templates) for analysis; S/N= >150, R=50000-67000, large spectral coverage
Initial Teff from Photometry, log(g) assuming M=1M
Spectroscopic determination: LTE, ionization equilibrium, no dependence on eq. width, no dependence on exc. potential
Sun plus 2 well-studied giants in literature for zero point correction: HD113226 (Vir), HD27371 (Hyades’ giant)
Parameters’ determination
Comparison of the stellar parameters with theoretical isochrones (Girardi et al. 2000) using a modified version of the Bayesian estimation of Jorgenson and Lindegren (2005) algorithm. The total probability distribution function of belonging to M,t space is computed from the Mv, Teff, [Fe/H] probabilities.
Sanity Checks
Several sanity checks were made: (B-V)-(B-V)o, Gravity, Radius
<(B-V)-(B-V)o> = -0.009 = 0.03
Teff-(B-V) transformation can be improved, known to be not suitable for cool stars
Sanity Checks
Spectro - log(g) > evolutionary log(g):known; non-LTE, strong dependence on : = 0.07 km/s --> log(g) = -0.2Effect on [Fe/H] negligible (FeI)
Red points: lunar occultation or long baseline interferometry. Agreement to better than 6%
Results
= 0.12 for M>1.2M and [Fe/H]~0
Age-Metallicity Relationship
•The youngest stars (age < 1 gyrs, 17.1 stars) are compatible with a single value
of [Fe/H] (sigma=0.09). • Spread become significant at higher ages; at 4 Gyrs much larger than measurement errors.
• AMR is flat up to the largest age; only ~ -0.2 -0.3 at 12 Gyrs
The results of the young bin are different from what found in main sequence surveys
Giants (and subgiants) seemson the other hand very good tracers of the young population
The cumulative [Fe/H]/age bin (t) is computed by weighting the measured [Fe/H] with the probability of belonging to t
STARS Hosting Planets
4 Stars (3 in South, 1 in the North) have been shown to host planets (Setiawan et al. 04, 05, Döllinger 06)
GIANTS hosting planets do not seem to be preferentially metal rich!