A 3 Dimensional Simulation of Common-Envelope Evolution of a Neutron Star with a 5~\msun\ and a 16~\msun\ Red Giant.
Session 65 -- Interacting Binaries: Compact Stars
Oral presentation, Thursday, January 13, 2:15-3:45, Salon V Room (Crystal Gateway)

## [65.08] A 3 Dimensional Simulation of Common-Envelope Evolution of a Neutron Star with a 5~\msun\ and a 16~\msun\ Red Giant.

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 neutron star companion, are presented. We use a 3 dimensional Smoothed Particle Hydrodynamic (SPH) code with an equation of state that includes the contributions of both gas and radiation. Two red giant models are used to show the dependence of the red giant stellar structure on the calculation results. The lower mass red giant has a mass of 5~\msun, a radius of $1.49 \times 10^{2}$~\rsun\ and a 0.67~\msun\ carbon-oxygen core. The higher mass red giant has a mass of 16~\msun, a radius of $6.59 \times 10^{2}$~\rsun\ and a 4.5~\msun\ helium-burning core. After placing a neutron star companion in a circular orbit at the edge of the red giant's envelope, tidal torques cause the orbit to decay. The neutron star quickly spirals into the red giant's envelope. After several dynamical times, the neutron star and red giant core are left in a tight orbit having given most of their orbital binding energy to the red giant envelope that surrounds them. We present several sets of snapshots of both stars' evolution. The snapshots take the form of density and velocity vector cross sections in and perpendicular to the orbital plane of the binary system. We discuss the difference in the results produced by the different stellar structure of the two red giant models.