Stellar Parameters and Photospheric Abundances of Late-G Giants: Properties of the Targets of the Okayama Planet Search Program
Towards clarifying the properties of late-G giants, for which we are currently conducting a planet-search project at Okayama Astrophysical Observatory, an extensive spectroscopic study has been performed for our first target sample of fifty-seven G6-G9 III stars, in order to establish the atmospheric parameters (Teff, log g, vt, and [Fe/H]), the stellar mass along with the evolutionary status, and the photospheric abundances of various elements. It was confirmed that the conventional spectroscopic method of parameter determination using Fe I / II lines with the assumption of LTE works successfully for these evolved stars. We determined the abundances (relative to the Sun) of 19 elements, and examined how their [X/Fe] ratios behave themselves with the run of [Fe/H]. While the trends appear to be similar to those exhibited by disk dwarfs for a number of elements, some elements (C, O, Na) showed appreciable anomalies, which may be interpreted as being due to a dredge-up of nuclear-processed material. Since the [Fe/H] values of these stars tend to be somewhat biased towards a subsolar regime, some mechanism of slightly reducing the metallicity might be suspected.