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

Abstract

We present a detailed spectroscopic analysis of horizontal branch stars in the globular cluster NGC 3201. We collected optical (4580–5330 Å), high-resolution (∼34,000), high signal-to-noise ratio (∼200) spectra for 11 RR Lyrae stars and one red horizontal branch star with the multifiber spectrograph M2FS with the 6.5 m Magellan telescope at the Las Campanas Observatory. From measured equivalent widths, we derived atmospheric parameters and abundance ratios for α (Mg, Ca, and Ti), iron-peak (Sc, Cr, Ni, and Zn), and s -process (Y) elements. We found that NGC 3201 is a homogeneous, monometallic ([Fe/H] = −1.47 ± 0.04), α -enhanced ([ α /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; and 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: V rad  = 494 ± 2 km s −1 ( σ = 8 km s −1 ).