The frequency by mass of Galactic carbon stars inferred from Gaia measurements of star cluster members

Abstract

We investigate the frequency of occurrence of Galactic carbon stars as a function of progenitor mass using Gaia data. Small number statistics limit fidelity, but C-star frequency agrees with that observed in the Magellanic Clouds (MCs) down to m ≈ 1.67 M⊙. At m ≈ 1.38 M⊙, the frequency rises by a factor of three even though the frequency appears to drop to zero for the MCs. In fact this is due to a lack of clusters at the key age range in the MCs. At m ≈ 1.24 M⊙ and below, no C-stars are observed, corresponding to ages older than 4 Gyr. Within uncertainties, C-star frequency in M 31 is consistent with that of the Galaxy and the MCs. We find an ambiguous C-star candidate at ∼7 M⊙.