The interaction between multi-dimensional convection and radial stellar pulsation

Abstract

We have developed a three-dimensional radiation hydrodynamics code to simulate the interaction of convection and pulsation in classical variable stars. One key goal is the ability to carry these simulations to full amplitude for comparison with observed light and velocity curves. The only previous multi-dimensional calculations were prevented from reaching full amplitude because of drift in the radial coordinate system, due to the algorithm defining radial movement of the coordinate system during the pulsation cycle. We remove this difficulty by defining our radial coordinate flow algorithm to require that the mass in a spherical shell remains constant for every time-step throughout the pulsation cycle. We present results from various tests and checks of our new numerical code SPHERLS such as comparison of our models pulsation periods with those of a linear adiabatic code and comparison to the analytic solution of a spherical blast wave. We have used our new code to perform 2D and 3D simulations of the interaction of radial pulsation and convection. We have made comparisons between light curves from our 2D convective simulations with observed light curves finding that our 2D simulated light curves are better able to match the observed light curve shape near the red edge of the RR Lyrae instability strip than light curves from previous 1D time dependent convective models. We examine the differences between the 2D and 3D convective flow patterns, finding stronger convective flows in 3D than 2D, but with only a small decrease in the 3D peak radial pulsation kinetic energy growth rates as compared to the 2D growth rates. Finally we make an early comparison between the 2D and 3D light curves near full amplitude.