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Current problems on horizontal branch stars |
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| Authors: | Filippina Caputo Vittorio Castellani |
| Institution: | 1. Laboratorio di Astrofisica Spaziale, Frascati, Italy 2. Astronomy Centre, University of Sussex, England 3. Istituto di Fisica, Università di Roma, Italy |
| Abstract: | Expected characteristics of RR Lyrae stars as a function of the evolutive parameters are reported. Results from both evolutionary and pulsational investigations are collected in a suitable form, to show the general constraints to any interpretative analysis of the observations. It is shown that the spread in luminosity among the RR Lyrae stars results a function of the original chemical composition. On this basis a set of independent indications is found, suggesting that the globular cluster ω Cen is more He-rich than M 3; agreement with the whole observational frame is attained ifY ωCen～0.35,Z ωCen～5×10?4 andY M3～0.25,Z M3～10?3. No mass loss is needed to account for the RR Lyrae stars observed in ω Cen. The results are discussed, and it is shown that M 13-type clusters can be just characterized by a larger value ofZ in comparison with ω Cen. It is suggested that variations in the original helium content of the order of ΔY～0.1 and a correlationZ=Z(t) can account for some well-observed galactic globular clusters, without allowing for mass loss in the redder HB stars belonging to each cluster. |
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