(Proposal ID) S15A-008

(PI) Takeda, Yoichi

(Proposal Title)
 Clarifying Red Giants Evolutionary Status in Reference to the  Kepler sample

(Abstract)
Clarifying the evolutionary status of red giants is very difficult since 
tracks of H-burning red giants (RG) and He-burning ones such as red-clump 
giants of two types (RC1, RC2) overlap in the HR diagram. However, Kepler's 
very high photometric precision detected their g-mode oscillation and 
successfully discriminated RG/RC1/RC2 from the differences of power spectra, 
which led to very accurate determinations of M and R (i.e., log g and age) 
for these Kepler-field giants. As the distiction of RG/RC1/RC2  is manifestly 
seen in the "trifid'' distribution in log g_{kepler} vs. M_{kepler} relation, 
there is a prospect that red giant stars may be distinguished from their 
positions in the log g vs. M diagram established in an ordinary way such as 
adopted by Takeda et al. (2008) (e.g., spectroscopic method with the help of 
theoretical evolutionary tracks).  To check this possibility, we intend to 
carry out conventional parameter determinations for Mosser et al.'s (2012) 
218 Kepler giants sample (with well-established M and log g) based on high-
dispersion spectra obtained with Subaru/HDS, in order to use them as 
calibration standards. Besides, we also determine the abundances of various 
elements to investigate the chemical evolution of the Galaxy, utilizing the 
merit of accurately known ages for these targets.