NONLINEAR RR LYRAE MODELS WITH NEW LIVERMORE OPACITIES

A. N. Cox recently showed that a 20% opacity decrease in the 20,000-30 .000 K region as indicated by the new Livermore OPAL opacities reconci les the discrepancy between pulsation and evolution masses of double-m ode RR Lyrae variables. Nonlinear hydrodynamic calculations were perfo rmed for RR Lyrae models of mass 0.75 M., 51 L.. and Z = 0.0001 (Oster hoff II type) including this opacity decrease. The Stellingwerf period ic relation method was used to converge the models to a limit cycle, a nd the Floquet matrix eigenvalues calculated to search for a tendency of the fundamental mode to grow from the full-amplitude overtone solut ion, and the overtone mode to grow from the full-amplitude fundamental solution, thereby predicting double-mode behavior. Models of T(eff) < 7000 K with the opacity decrease have positive fundamental-mode growt h rates in the overtone solution, in contrast to earlier results by Ho dson and Cox (1982), and models with T(eff) > 7000 have positive 1st o vertone growth rates in the fundamental-mode solution, but double-mode behavior was not found.