The calcium abundance of RR Lyrae variables in omega Centauri and M22.
Abstract
Freeman and Rodgers observed 25 RR Lyrae variables in w Cen and reported a range in calcium abundance from [Ca/H] = -0.4 to - 1.6. This result, however, has been difficult to reconcile with other recent studies of the giant branch of w Cen. With a model-atmosphere grid covering the physical parameters expected for RR Lyrae variables, we have reanalyzed Freeman and Rodgers's data, using their basic method of theoretical relations among the equivalent widths of the K, Hfl, and H8 lines and [Ca/H] but with an alternative, synthetic-spectrum approach to the calibration of these relations. When interpreted with our calibration, the data yield a range in calcium abundance from [Ca/H] = - 1.0 to - 1.9 for the w Cen RR Lyrae variables. Our calibration applied to the M22 data of Butler et al. gives [Ca/H] = -1.25 for M22. Subject headings: stars: abundances - stars: RR Lyrae
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1978
- DOI:
- 10.1086/156556
- Bibcode:
- 1978ApJ...225..908M
- Keywords:
-
- Abundance;
- Calcium;
- Cepheid Variables;
- Stellar Atmospheres;
- Stellar Spectrophotometry;
- Line Spectra;
- Spectral Line Width;
- Stellar Spectra;
- Astrophysics;
- Calcium:RR Lyrae Stars;
- Globular Clusters:RR Lyrae Stars