Spectroscopic comparative study of the red giant binary system gamma Leonis A and B

TL;DR

This study compares the physical and chemical properties of the binary system gamma Leo A and B using high-resolution spectra, revealing their evolutionary status, chemical compositions, and the impact of planet formation on surface abundances.

Contribution

It provides the first detailed spectroscopic comparison of both components, including revised stellar and planetary parameters, and assesses the influence of planet presence on stellar surface chemistry.

Findings

Both stars are red clump giants with similar chemical compositions.

The planet's mass around gamma Leo A has been increased by about 20%.

Surface chemical abundances are unaffected by the planet's presence.

Abstract

Gamma~Leo is a long-period visual binary system consisting of K0III (A) and G7III (B) giants, in which particular interest is attracted by the brighter A since the discovery of a planet around it. While detailed spectroscopic comparative study of both components would be worthwhile (e.g., for probing any impact of planet formation on chemical abundances), such a research seems to have been barely attempted as most available studies tend to be biased toward A. Given this situation, the physical properties of A and B along with their differences were investigated based on high-dispersion spectra in order to establish their stellar parameters, evolutionary status, and surface chemical compositions. The following results were obtained. (1) The masses were derived as ~1.7Msun and ~1.6Msun for A and B, respectively, both of which are likely to be in the stage of red clump giants after He-ignition. The mass of the planet around A has also been revised as m*sin(i) = 10.7M_Jupiter (increased by ~20%). (2) These are normal giants of subsolar metallicity ([Fe/H]~-0.4) belonging to the thin-disk population. (3) A as well as B show moderate C deficiency and N enrichment, which are in compatible with the prediction from the standard stellar evolution theory. (4) The chemical abundances of 26 elements are practically the same within <~0.1dex for both components, which implies that the surface chemistry is not appreciably affected by the existence of a planet in A.