Thermal Stability of White Dwarfs Accreting Hydrogen‐rich Matter and Progenitors of Type Ia Supernovae

We revisit the properties of white dwarfs accreting hydrogen-rich matter byconstructing steady-state models, in which hydrogen shell burning consumeshydrogen at the same rate as the white dwarf accretes it. We obtain suchsteady-state models for various accretion rates and white dwarf masses. Weconfirm that these steady models are thermally stable only when the accretionrate is higher than \sim 10^{-7} M_sun/yr. We show that recent models of``quiescent burning'' in the ``surface hydrogen burning'' at a much wider rangeof accretion rates results from the too large zone mass in the outer part ofthe models; hydrogen burning must occur in a much thinner layer. A comparisonof the positions on the HR diagram suggests that most of the luminous supersoftX-ray sources are white dwarfs accreting matter at rates high enough that thehydrogen burning shell is thermally stable. Implications on the progenitors ofType Ia supernovae are discussed.Comment: to appear in the Astrophysical Journal, 8 pages including 5 figure