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!