Inconsistency of Chemical Properties of Stellar Populations in the Thick Disk Subsystem of Our Galaxy

V. A. Marsakov, V. V. Koval', M. L. Gozha

Published 2020-02-25Version 1

Using modern published data on velocities and spectroscopic definitions of chemical elements in stellar objects of the Galaxy, we investigated the relationship of chemical composition with the kinematics of different populations. The paper shows that the old stellar populations of the Galaxy, belonging (by the kinematic criterion) to the thick disk subsystem---globular clusters, field variables of the type RR Lyrae (lyrids), as well as close F--G dwarfs and field giants, have different chemical composition. In particular, the dwarfs and giants of the field are on average more metallic than the globular clusters and lyrids of the field. Moreover, the relative abundances of $\alpha$-elements in the range $\rm{[Fe/H]} > -1.0$ are the highest for globular clusters, and are the lowest for for field variables of the RR Lyrae type. Based on the analysis of the nature of the dependences of [$\alpha$/Fe] on [Fe/H] for these objects it was suggested that the thick disk subsystem in the Galaxy is composite and at least three components exist independently within it. The oldest one includes metal-rich globular clusters that formed from a single proto-galactic cloud shortly after the start of type Ia supernovae outbursts. Then the subsystem of field stars of a thick disk was formed as a result of ``heating'' of stars of already formed thin disk of the Galaxy by a rather massive dwarf satellite galaxy that fell on it. And finally, subsystems of field stars with the kinematics of not only a thick, but even a thin disk that fell on the Galaxy from this captured satellite galaxy.