Stellar Parameters and Elemental Abundances of Late-G Giants

TL;DR

This study comprehensively analyzes the stellar parameters and chemical abundances of 322 late-G giants, revealing insights into their properties, evolution, and the relationship between metallicity and planet hosting.

Contribution

It provides the first extensive chemical and physical characterization of intermediate-mass late-G giants, including their relation to planet presence and evolutionary processes.

Findings

Planet-host giants have similar metallicity distributions as non-planet-host giants.

Metallicity of these giants is generally lower than that of dwarfs of the same age.

Surface abundances of C, O, and Na are affected by deep envelope mixing during evolution.

Abstract

The properties of 322 intermediate-mass late-G giants (comprising 10 planet-host stars) selected as the targets of Okayama Planet Search Program, many of which are red-clump giants, were comprehensively investigated by establishing their various stellar parameters (atmospheric parameters including turbulent velocity fields, metallicity, luminosity, mass, age, projected rotational velocity, etc.), and their photospheric chemical abundances for 17 elements, in order to study their mutual dependence, connection with the existence of planets, and possible evolution-related characteristics. The metallicity distribution of planet-host giants was found to be almost the same as that of non-planet-host giants, making marked contrast to the case of planet-host dwarfs tending to be metal-rich. Generally, the metallicities of these comparatively young (typical age of ~10^9 yr) giants tend to be somewhat lower than those of dwarfs at the same age, and super-metal-rich ([Fe/H] > 0.2) giants appear to be lacking. Apparent correlations were found between the abundances of C, O, and Na, suggesting that the surface compositions of these elements have undergone appreciable changes due to dredge-up of H-burning products by evolution-induced deep envelope mixing which becomes more efficient for higher-mass stars.