Metallicity Effects on RR Lyrae Variables

Since the seminal paper of Preston, the existence of a metal-rich component among the RR Lyrae variable stars belonging to the solar neighborhood has become a well-known observational fact. In this investigation the effects of heavy-element abundance on theoretical observables is studied for both fundamental and first-overtone pulsators at fixed mass (M/M☉ = 0.53) and luminosity level [log (L/L☉) = 1.51]. In order to cover the observed range of RR Lyrae metallicity, the nonlinear models have been computed by adopting three different metal contents (Z = 0.0001, 0.001, and 0.02). It has been found that the bolometric amplitude of first-overtone pulsators decreases as the metallicity increases, whereas for fundamental pulsators the amplitude is positively correlated with the metal abundance.

[1]  Christopher W. Stubbs,et al.  The MACHO Project LMC Variable Star Inventory.II.LMC RR Lyrae Stars- Pulsational Characteristics and Indications of a Global Youth of the LMC , 1996 .

[2]  A. Layden.  The Metallicities and Kinematics of RR Lyrae Variables.II. Galactic Structure and Formation from Local Stars , 1995 .

[3]  Robert F. Stellingwerf,et al.  Pulsation and stability of RR Lyrae stars. 1: Instability strip , 1994 .

[4]  N. Suntzeff,et al.  Summary of Delta S Metallicity Measurements for Bright RR Lyrae Variables Observed at Lick Observatory and KPNO between 1972 and 1987 , 1994 .

[5]  M. Seaton,et al.  Opacities for stellar envelopes , 1994 .

[6]  S. Kanbur,et al.  Comparative pulsation calculations with OP and OPAL opacities , 1994 .

[7]  M. Seaton.  Fitting and smoothing of opacity data , 1993 .

[8]  Michael Gehmeyr,et al.  On nonlinear radial oscillations in convective RR Lyrae stars. III: A full-amplitude investigation of the red edge , 1993 .

[9]  F. Rogers,et al.  Radiative atomic Rosseland mean opacity tables , 1992 .

[10]  J. Buchler,et al.  Toward a Resolution of the Bump and Beat Cepheid Mass Discrepancies , 1992 .

[11]  A. N. Cox.  Masses of RRd Variables Using Livermore OPAL Opacities , 1991 .

[12]  R. Stothers,et al.  Type II Cepheids - A comparison of theory with observations , 1981 .

[13]  R. Stellingwerf.  Nonlinear effects in double-mode Cepheids , 1975 .

[14]  David R. Alexander,et al.  Low-Temperature Rosseland Opacities , 1975 .

[15]  I. Iben,et al.  On the Location of Pulsational Blue Edges and Estimates of the Luminosity and Helium Content of RR Lyrae Stars , 1972 .

[16]  R. Christy,et al.  A study of pulsation in RR Lyrae models. , 1966 .

[17]  George W. Preston,et al.  A Spectroscopic Study of the RR Lyrae Stars. , 1959 .

[18]  R. Stellingwerf.  Modal stability of RR Lyrae stars. , 1975 .