ON omega CENTAURI AND ITS RRc STARS

Authors

Norman R. Simon, University of Nebraska - LincolnFollow

Document Type

Article

Date of this Version

9-1-1990

Citation

THE ASTROPHYSICAL JOURNAL, 360: 119-128,1990 September 1

Comments

Copyright 1990 The American Astronomical Society. All rights reserved.

Abstract

Masses, temperatures, and absolute luminosities are proposed for a large sample of RRc stars in the globular cluster w Centauri. Our technique uses three observed quantities: period, relative luminosity, and Fourier phase ϕ₃₁ interpreting them in the light of linear and hydrodynamic pulsation models. The masses we obtain agree with those of the RRd stars in other clusters, and our derived parameters pass a number of tests which are independent of the derivation: (1) we reproduce the observed slope, ∂ϕ₃₁/∂ log P, of the ϕ_{31 -}period diagram; (2) the values we obtain for M, T., and L locate the w Cen RRc stars in the first overtone instability strip, just where they belong; (3) our derived parameters are shown to be consistent with the fact that w Cen contains no RRd stars. However, our results not only disagree with current horizontal branch models, but also imply that the canonical slope of the log T_e versus B - V relation (obtained from static model atmospheres) is too steep by a factor of 2, at least as applied to the RRc stars. Some additional results are presented which bear on the confrontation between evolution and pulsation theory: (1) it is shown that the disagreement between the RRd masses and those based on horizontal branch calculations cannot be reconciled by reasonable changes in metallicity or opacity; (2) we find essentially no correlation between the masses of the w Cen RRc stars and their metallicities, and we demonstrate that this circumstance cannot be due to late redward evolution by the RR Lyrae stars of lower mass; and (3) the mass-luminosity relation obtained by our method for three RRc field stars is shown to be consistent with the results of a Baade-Wesselink analysis, but not with horizontal branch models. Finally, we briefly discuss the question of globular cluster ages and calculate an age for w Centauri based upon its RRc stars.