A 3 Dimensional Numerical Simulation of the Common-Envelope Evolution of a Red Giant and a White Dwarf.
Session 6 -- Binary Stars
Display presentation, Monday, 30, 1994, 9:20-6:30

## [6.03] A 3 Dimensional Numerical Simulation of the Common-Envelope Evolution of a Red Giant and a White Dwarf.

J. L. Terman, R. E. Taam (Northwestern U.), L. Hernquist (UCSC/UCO)

The results of our calculations which investigate the common-envelope evolution of a red giant and a dwarf companion are presented. We use a 3 dimensional Smoothed Particle Hydrodynamics (SPH) code with a red giant model consisting of 10,000 particles. After constructing a red giant with a mass of $9.30 \times 10^{33}$ g and a radius of $8.4 \times 10^{12}$ cm, we put it and a $1.86 \times 10^{33}$ g dwarf companion into a Roche potential. We then apply a drag to the dwarf that forces it to spiral in until it is at the edge of the red giant's atmosphere. At this point, we turn off the drag, and the evolution of the model proceeds naturally. The spiral in takes the form of a very eccentric, rapidly decaying orbit. Within several dynamical times, the dwarf and the red giant core are left in a tight orbit with a significant fraction of the red giant's envelope left unbound. We present several sets of snapshots of the evolution of the two stars from the time that drag is turned off to the time that the two cores settle into a tight orbit. The snapshots take the form of density and velocity cross sections in and perpendicular to the orbital plane of the binary system.