Mass evaluation for red giant stars based on the spectroscopically determined atmospheric parameters

The mass (M) of a star can be evaluated from its spectroscopically determined effective temperature (T _eff) and metallicity ([Fe/H]) along with the luminosity (L; derived from parallax), while comparing them with grids of theoretical evolutionary tracks. It has been argued, however, that such a track-based mass (M_trk) may tend to be overestimated for the case of red giants. Meanwhile, there is an alternative approach of evaluating mass (M_gLT) directly from surface gravity (g), L, and T_eff. The practical reliability of M_gLT was examined for ~100 benchmark giants in the Kepler field, for which atmospheric parameters are already determined and the reliable mass (M_seis) along with the evolutionary status are known from asteroseismology. In addition, similar check was also made for the accuracy of M_trk for comparison. It turned out that, while a reasonable correlation is seen between M_gLT and M_seis almost irrespective of the stellar property, its precision is rather insufficient because log(M_gLT/M_seis) distributes rather widely within ~+/-0.2--0.3dex. In contrast, the reliability of M_trk was found to depend on the evolutionary status. Although M_trk and M_seis are satisfactorily consistent with each other (typical dispersion of log(M_trk}/M_seis) is within ~+/-0.1dex) for H-burning red giants as well as He-burning 2nd clump giants of higher mass, M_trk tends to be considerably overestimated as compared to M_seis by up to ~<0.4~dex for He-burning 1st clump giants of lower mass. Accordingly, M_gLT and M_trk are complementary with each other in terms of their characteristic merit and demerit.

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