Spectral Analysis of Binary Pre-white Dwarf Systems

Abstract

Short period double degenerate white dwarf (WD) binaries with periodsof less than ∼1 day are considered to be one of the likely progenitors of type Ia super-novae. These binaries have undergone a period of common envelope evolution. If thecore ignites helium before the envelope is ejected, then a hot subdwarf remains priorto contracting into a WD. Here we present a comparison of two very rare systems thatcontain two hot subdwarfs in short period orbits. We provide a quantitative spectro-scopic analysis of the systems using synthetic spectra from state-of-the-art non-LTEmodels to constrain the atmospheric parameters of the stars. We also use these modelsto determine the radial velocities, and thus calculate dynamical masses for the stars ineach system.