Chemical Compositions of Field and Globular Cluster RR Lyrae Stars: I. NGC 3201

TL;DR

This study provides a detailed spectroscopic analysis of RR Lyrae stars in NGC 3201, revealing a homogeneous, metal-poor, alpha-enhanced cluster with chemical properties similar to other old halo populations.

Contribution

First detailed high-resolution spectroscopic analysis of RR Lyrae stars in NGC 3201, including atmospheric parameters and elemental abundances, with a new radial velocity estimate.

Findings

NGC 3201 is mono-metallic with [Fe/H]=-1.47

Cluster shows alpha-enhancement with [{ extalpha}/Fe]=0.37

RR Lyrae stars have chemical properties similar to other old halo stars

Abstract

We present a detailed spectroscopic analysis of horizontal branch stars in the globular cluster NGC 3201. We collected optical (4580-5330 A), high resolution (~34,000), high signal-to-noise ratio (~200) spectra for eleven RR Lyrae stars and one red horizontal branch star with the multifiber spectrograph M2FS at the 6.5m Magellan telescope at the Las Campanas Observatory. From measured equivalent widths we derived atmospheric parameters and abundance ratios for {\alpha} (Mg, Ca, Ti), iron peak (Sc, Cr, Ni, Zn) and s-process (Y) elements. We found that NGC 3201 is a homogeneous, mono-metallic ([Fe/H]=-1.47 +- 0.04), {\alpha}-enhanced ([{\alpha}/Fe]=0.37 +- 0.04) cluster. The relative abundances of the iron peak and s-process elements were found to be consistent with solar values. In comparison with other large stellar samples, NGC 3201 RR Lyraes have similar chemical enrichment histories as do those of other old (t>10 Gyr) Halo components (globular clusters, red giants, blue and red horizontal branch stars, RR Lyraes). We also provided a new average radial velocity estimate for NGC 3201 by using a template velocity curve to overcome the limit of single epoch measurements of variable stars: Vrad=494 +- 2 km s-1({\sigma}=8 km s-1).