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| Paper: |
RR Lyrae Variables in Globular Clusters and the Second-Parameter Phenomenon |
| Volume: |
135, A Half Century of Stellar Pulsation Interpretations: a Tribute to Arthur N. Cox |
| Page: |
41 |
| Authors: |
Catelan, M.; Sweigart, A. V.; Borissova, J. |
| Abstract: |
Recent developments suggest that several parameters, besides metallicity (the "first" parameter), may be affecting the morphology of the horizontal branch in Galactic globular clusters. Current second-parameter candidates include age, mass loss on the red giant branch, envelope helium abundance, helium-core mass at the helium flash, and abundance ratios of the alpha-capture elements. An important limitation in analyzing the second- parameter phenomenon is the fact that any of these candidates can equally well account for the observed differences in the horizontal-branch morphology, if only in an ad-hoc way. These candidates can, however, be divided into two main categories, in the sense that some of them are expected to affect the luminosity of the horizontal branch, while others---in particular age and mass loss---are not. With this in mind, we propose to employ the period shifts of RR Lyrae variables as a vertical diagnostic of horizontal-branch morphology. In particular, we perform a preliminary analysis of the observational data, especially for clusters with bimodal horizontal-branch distributions, in an attempt to search for the imprints of variations in the second-parameter candidates other than age and/or mass loss. |
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