The Chemical Compositions of Variable Field Horizontal Branch Stars: RR Lyrae Stars

TL;DR

This study provides a detailed chemical abundance analysis of 11 RR Lyrae stars, revealing their compositions, microturbulence behavior, and evolutionary status, with a new method for temperature determination across pulsation phases.

Contribution

A novel approach to determine initial effective temperatures at specific pulsational phases and insights into abundance ratios and microturbulence variations in RR Lyrae stars.

Findings

Abundance ratios are consistent with similar metallicity field stars.

TY Gru is uniquely enriched in n-capture elements.

Microturbulence varies with phase similarly to theoretical predictions.

Abstract

We present a detailed abundance study of 11 RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic.High resolution and high S/N echelle spectra of these variables were obtained with 2.5 m du Pont telescope at the Las Campanas Observatory. We obtained more than 2300 spectra, roughly 200 spectra per star, distributed more or less uniformly throughout the pulsational cycles. A new method has been developed to obtain initial effective temperature of our sample stars at a specific pulsational phase. We find that the abundance ratios are generally consistent with those of similar metallicity field stars in different evolutionary states and throughout the pulsational cycles for RR Lyrae stars. TY Gru remains the only n-capture enriched star among the RRab in our sample. A new relation is found between microturbulence and effective temperature among stars of the HB population. In addition, the variation of microturbulence as a function of phase is empirically shown to be similar to the theoretical variation. Finally, we conclude that the derived teffand log g values of our sample stars follow the general trend of a single mass evolutionary track.