Galactic-Field Metal-Rich RR~Lyrae Variables: Features of Kinematics and Abundances of Selected Chemical Elements

TL;DR

This paper analyzes the chemical abundances and kinematic properties of metal-rich Galactic-field RR Lyrae stars, revealing unique chemical signatures and suggesting some may have extragalactic origins.

Contribution

It provides new insights into the chemical composition and kinematic characteristics of metal-rich RR Lyrae stars, highlighting potential extragalactic origins.

Findings

Lower alpha-element abundances compared to similar metallicity stars

Some stars show very low sodium, aluminum, and nickel abundances

Orbital parameters typical of Galactic disk objects

Abstract

We present an analysis of the relative abundance features of a number of chemical elements in the atmospheres of metal-rich ($\rm{[Fe/H]} > -1.0$) Galactic-field RR~Lyrae variable stars and the kinematic characteristics of these stars. We have previously shown that the relative abundances of some $\alpha$-elements: magnesium, silicon, calcium, and to a greater extent of titanium, as well as yttrium and scandium in such stars are lower than in most of other types of stars, bearing similar metallicity. It is found here that some of these metal-rich RR~Lyrae stars also have very low relative abundances of sodium, aluminum and nickel. The orbital parameters of all the metal-rich RR~Lyrae variables studied in this paper are typical of the Galactic thin or thick disk objects, however, unusual chemical composition let us to suggests a possible extragalactic origin for some of them.