Common Envelope Evolution for Helium-Star Neutron-Star Binaries

After a neutron star survives common envelope evolution with a massive star, the helium-star remnant may undergo another phase of mass transfer: caseBB. This mass transfer may become dynamically unstable and initiate another common envelope phase with the helium star and neutron star pair. In order to characterize the conditions for which such binaries survive common envelope evolution, we model this inspiral with 1D MESA models for the helium star, accounting for accretion and gravitational drag in the equation of motion. We also estimate the gravitational wave emission for cases in which the neutron star merges with the core of the helium star.