Modelling the AM CVn and double detonation supernova progenitor binary system CD-3011223

We present a detailed modelling study of CD-30 degrees 11223 (CD-30), a hot subdwarf (sdB)-white dwarf (WD) binary identified as a double detonation supernova progenitor, using the open-source stellar evolution software MESA. We focus on implementing binary evolution models carefully tuned to match the observed characteristics of the system including logg and T-eff. For the first time, we account for the structure of the hydrogen envelope throughout the modelling, and find that the inclusion of element diffusion is important for matching the observed radius and temperature. We investigate the two sdB mass solutions (0.47 and 0.54 M-circle dot) previously proposed for this system, strongly favouring the 0.47 M-circle dot solution. The WD cooling age is compared against the sdB age using our models, which suggest an sdB likely older than the WD, contrary to the standard assumption for compact sdB-WD binaries. Subsequently, we propose a possible alternate formation channel for CD-30. We also perform binary evolution modelling of the system to study various aspects such as mass transfer, orbital period evolution, and luminosity evolution. Our models confirm CD-30 as a double detonation supernova progenitor, expected to explode approximate to 55 Myr from now. The WD accretes an approximate to 0.17 M-circle dot thick helium shell that causes a detonation, leaving a 0.30 M-circle dot sdB ejected at approximate to 750 kms(-1). The final 15 Myr of the system are characterized by helium accretion which dominates the system luminosity, possibly resembling an AM CVn-type system.