Helium star donors to thermonuclear supernovae

We perform binary evolution calculations of helium star - carbon-oxygen white dwarf binaries using the stellar evolution code MESA. We focus on 1-2 Msun He stars that undergo thermal-timescale mass transfer. We survey the initial binary parameters (orbital period and He star mass) and determine which systems can evolve towards thermonuclear supernovae. Our time-dependent calculations resolve the stellar structures of both binary components, which allows accurate detection of the occurrence of off-center carbon ignitions. We find systems that successfully reach explosion generally have orbital periods of hours; it will be useful to understand the MW population of He star - WD binaries with these properties. We also describe the observational appearance of these systems near the time of explosion as they may be detectable in pre-explosion images of supernovae.