Numerical Simulations of the Onset and Stability of Dynamical Mass Transfer in Binaries

Hydrodynamical simulations of semi-detached, polytropic binary stars are presented in an effort to study the onset and stability of dynamical mass transfer events. Initial, synchronously rotating equilibrium models are constructed using a self-consistentfield technique and then evolved with an Eulerian hydrodynamics code in a fully selfconsistent manner. We describe code improvements introduced over the past few years that permit us to follow dynamical mass-transfer events through more than 30 orbits. Mass-transfer evolutions are presented for two different initial configurations: A dynamically unstable binary with initial mass ratio (donor/accretor) q0 = 1.3 that leads to a complete merger in ∼ 10 orbits; and a double-degenerate binary with initial mass ratio q0 = 0.5 that, after some initial unstable growth of mass transfer, tends to separate as the mass-transfer rate levels off. Subject headings: Numerical Hydrodynamics — Interacting binaries: accretion —Masstransfer — Stability — Double White Dwarfs