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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)
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GIANTS hosting planets do not seem to be preferentially metal rich!