New Initiatives on RR Lyrae Chemical Compositions

TL;DR

This paper discusses recent advances in understanding the chemical compositions of RR Lyrae stars, including detailed spectroscopic studies and their implications for Galactic halo structure and stellar evolution.

Contribution

It presents new spectroscopic data on RR Lyrae stars, explores their orbital motions, and compares different subclasses to enhance knowledge of Galactic halo formation.

Findings

Detection of neutron-capture enhancement in TY Gru

Spectroscopic analysis of 10 additional RR Lyrae stars

Contrast of atmospheric compositions between RRc and RRab stars

Abstract

The serendipitous discovery by Preston and colleagues of the neutron-capture-enhanced RR Lyrae variable star TY Gru (a.k.a. CS 22881-071 in the "HK" survey of very metal-poor halo stars) has resulted in a growing set of initiatives on the chemical compositions of RR Lyrae stars and their application to broader topics in Galactic halo structure. Here we summarize the main aspects of our work on TY Gru, including a new discussion of our search for possible orbital motion of this star around a putative unseen companion. Then we describe a few of the results of a newly-completed intensive spectroscopic investigation of 10 additional field RR Lyr stars. We finish by outlining current projects that seek to contrast the atmospheres and chemical compositions of RRc stars with those of the RRab stars, and that employ a much larger RRab sample in a chemo-dynamical study of Galactic halo RR Lyr.