Relationship between the Elemental Abundances and the Kinematics of Galactic-Field RR Lyrae Stars

Abstract

Data of our compiled catalog containing the positions, velocities, and metallicities of 415 RR~Lyrae variable stars and the relative abundances [el/Fe] of 12~elements for 101 RR~Lyrae stars, including four $\alpha$~elements (Mg, Ca, Si, and Ti), are used to study the relationships between the chemical and spatial--kinematic properties of these stars. In general, the dependences of the relative abundances of $\alpha$~elements on metallicity and velocity for the RR~Lyrae stars are approximately the same as those for field dwarfs. Despite the usual claim that these stars are old, among them are representatives of the thin disk, which is the youngest subsystem of the Galaxy. Attention is called to the problem of low-metallicity RR~Lyrae stars. Most RR~Lyrae stars that have the kinematic properties of thick disk stars have metallicities $[Fe/H]<-1.0$ and high ratios [$\alpha$/Fe]$\approx 0.4$, whereas only about 10\,\% of field dwarfs belonging to the so-called "low-metallicity tail" have this chemical composition. At the same time, there is a sharp change in [$\alpha$/Fe] in RR~Lyrae stars belonging just to the thick disk, providing evidence for a long period of formation of this subsystem. The chemical compositions of SDSS J1707+58, V455 Oph, MACHO 176.18833.411, V456 Ser, and BPS CS 30339--046 do not correspond to their kinematics. While the first three of these stars belong to the halo, according to their kinematics, the last two belong to the thick disk. It is proposed that they are all most likely extragalactic, but the possible appearance of some of them in the solar neighborhood as a result of the gravitational action of the bar on field stars cannot be ruled out.

16 pages, 3 figures, 1 table

References in corpus (5)

• On a new theoretical framework for RR Lyrae stars I: the metallicity dependence
• A Possible Origin of the Mass-Metallicity Relation of Galaxies
• Chemical abundances of solar neighborhood RR Lyrae stars
• A high-velocity bulge RR Lyrae variable on a halo-like orbit
• Chemical abundances in a high velocity RR Lyrae star near the bulge

Cited by in corpus (11)

• Chemo-kinematics of the $Gaia$ RR Lyrae: the halo and the disc
• Evidence for Galactic disc RR~Lyrae stars in the Solar neighbourhood
• RR Lyrae From Binary Evolution: Abundant, Young and Metal-Rich
• Local RR Lyrae Stars: native and alien
• Probing the Galactic Halo with RR Lyrae Stars. II. The Substructures of the Milky Way
• The GALAH survey: Tracing the Milky Way's formation and evolution through RR Lyrae stars
• Masses of RR Lyrae Stars with Different Chemical Abundances in the Galactic Field
• The Chemical Composition of Globular Clusters of Different Nature in our Galaxy
• Globular Clusters of the Galaxy: Chemical Composition vs Kinematics
• Peculiarities of Abundances of Selected Elements in Metal-Rich Field RR Lyrae Stars
• Inconsistency of Chemical Properties of Stellar Populations in the Thick Disk Subsystem of Our Galaxy