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

γ Leo is a long-period visual binary system consisting of K0 iii (A) and G7 iii (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 ∼ 1.7 M_⊙ and ∼ 1.6 M_⊙ 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_psin i_p≃ 10.7 M_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 ≲ 0.1 dex for both components, which implies that the surface chemistry is not appreciably affected by the existence of a planet in A.