Hydrodynamical Simulations of Hα Emission in Algol Binaries

Abstract

Two-dimensional hydrodynamical simulations of mass transfer in short period Algol type binaries were performed using the numerical code VH−1. This code uses the Piecewise Parabolic Method with a Lagrangian Remap. Our version of the code also accounts for radiative cooling processes. The purpose of performing the simulations was to study the Hα emission from circumstellar gas in the Algols. Using observational evidence from the literature to constrain the gas stream properties, hydrodynamical maps of the Hα emissivity in the two systems β Per (P = 2.87d) and TT Hya (P = 6.95d) were made in both Cartesian and velocity coordinates from the simulation data. The velocity maps were then compared to Doppler tomograms constructed from observed Hα line emission in these systems. Since the tomograms cannot be directly transformed to maps of emission in spatial coordinates, the simulated Cartesian maps enable us to interpret the dynamical processes which produce the features observed in the Doppler tomograms. We find that the simulations produce asymmetric accretion structures with many features similar to those found in the Doppler tomograms of Algol systems.