Transcript giants1
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 accurate radial 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 Northern Sample Southern Sample Subgiants, RGB stars, Clump Stars, early AGB RV: Statistics Southern Stars 13 Binaries (17%) 21 Constant (27%) Northern Stars 11 Binaries (16%) 6 Constant (9%) 43 Variable (56%) 9 Long Period (15%) 3 Planets confirmed 1 Planet confirmed 8 Activity Modulation 36 Short Period (60%) or pulsation : Ca II and/or bisector variations with Period RV~22 m/sec RV~5 m/sec RV along the H-R diagram Does RV depends on the absolute stellar magnitude (Southern Sample) ? •BD comp. Planets Apparent trends are ‘contaminated’ by different physical causes 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 Teff-(B-V) transformation can be improved, known to be <(B-V)-(B-V)o> = -0.009 = 0.03 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) = -0.2 Effect 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 cumulative [Fe/H]/age bin (t) is computed by weighting the measured [Fe/H] with the probability of belonging to t •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) seems on the other hand very good tracers of the young population 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!