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
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.