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Spectroscopic parameters (effective temperature, metallicity, etc) weredetermined for a large sample of ~100 red giants in the Kepler field, for whichmass, radius, and evolutionary status had already been asteroseismologicallyestablished. These two kinds of spectroscopic and seismic information sufficeto define the position on the "luminosity versus effective temperature" diagramand to assign an appropriate theoretical evolutionary track to each star.Making use of this advantage, we examined whether the stellar location on thisdiagram really matches the assigned track, which would make an interestingconsistency check between theory and observation. It turned out thatsatisfactory agreement was confirmed in most cases (~90%, though appreciablediscrepancies were seen for some stars such as higher-mass red-clump giants),suggesting that recent stellar evolution calculations are practically reliable.Since the relevant stellar age could also be obtained by this comparison, wederived the age-metallicity relation for these Kepler giants and found thefollowing characteristics: (1) The resulting distribution is quite similar towhat was previously concluded for FGK dwarfs. (2) The dispersion of metallicityprogressively increases as the age becomes older. (3) Nevertheless, the maximummetallicity at any stellar age remains almost flat, which means the existenceof super/near-solar metallicity stars in a considerably wide age range from~(2--3)x 10^8~yr to ~10^10~yr.

Fundamental stellar parameters and age-metallicity relation of Kepler red giants in comparison with theoretical evolutionary tracks