THE CHEMICAL-COMPOSITION OF FIELD RR LYRAE STARS .1. IRON AND CALCIUM

Citation
Dl. Lambert et al., THE CHEMICAL-COMPOSITION OF FIELD RR LYRAE STARS .1. IRON AND CALCIUM, The Astrophysical journal. Supplement series, 103(1), 1996, pp. 183-210
Citations number
104
Categorie Soggetti
Astronomy & Astrophysics
ISSN journal
00670049
Volume
103
Issue
1
Year of publication
1996
Pages
183 - 210
Database
ISI
SICI code
0067-0049(1996)103:1<183:TCOFRL>2.0.ZU;2-5
Abstract
Iron and calcium abundances for 18 local field RR Lyrae stars are obta ined from high-resolution spectra taken near minimum light. Abundance analyses are presented using model atmospheres defined by published ph otometry. Analyses were also undertaken using model atmospheres chosen to fit the excitation equilibrium of Fe I and the ionization equilibr ium of iron. Systematic differences between the two analyses are discu ssed. Contributions of non-LTE effects are assessed quantitatively. Th e Fe abundance is given most reliably by Fe II lines analyzed with the photometric models, and the Ca abundance is probably best given by co mbining this Fe abundance with the Ca/Fe ratio given by the photometri c(or the spectroscopic) model atmospheres and the Ca I and Fe I lines. The Ca/Fe ratio of these RR Lyrae stars follows the well-known variat ion of [Ca/Fe] with [Fe/H] found for dwarfs and giants; most notably, the metal-rich ([Fe/H] similar or equal to 0)RR Lyrae stars do not hav e an anomalous Ca/Fe ratio. New calibrations are presented of the Delt a S-[Fe/H] and M(V)-[Fe/H] relations. Appendices provide critical eval uations of published gf-values for the Fe I and Fe II lines used in th is analysis.