An Intensive HST/COS Study of 31 CV WDs

Abstract

Accretion is the key ingredient in the evolution of white dwarfs (WDs) in cataclysmic variables (CVs), with important implications for their potential as progenitors for Type Ia Supernovae. The effective temperature (T<SUB>eff</SUB>) gives a direct measure of the average accretion rate and we report here the T<SUB>eff</SUB> measurement for 31 CV WDs, observed as a part of a 122 orbit HST program. The HST spectra alone cannot resolve the degeneracy between T<SUB>eff</SUB> and the surface gravity log g, and we will use phase-resolved X-Shooter observations to (i) measure the mass ratio of the CVs from the reflex motion of both the WD and the donor star (ii) to establish the spectral energy distribution (SED), which constrains both T<SUB>eff</SUB> and log g. Combining the X-Shooter and HST data, we can measure the WD masses to a few percent, and will be able to answer the question whether accreting CV WDs grow in mass.