The Single-Degenerate Scenario for Type Ia SNe in Cosmic Perspective

Abstract

The occurrence and properties of Type Ia supernovae (SNe Ia) in single-degenerate binary systems (white dwarf [WD] + nondegenerate companion) is examined for galaxies of different types, and as a function of redshift. The rates and characteristics (peak luminosities, expansion velocities of the ejecta) expected from the explosion of mass-accreting WDs in symbiotic systems and "helium star cataclysmics" are found to be different from those arising in another class of candidate systems: cataclysmic-like (contact) systems (CLS), where a CO WD accretes hydrogen on a thermal time scale from a Roche-lobe filling main-sequence or subgiant companion. We derive the evolution of the SNe Ia rate and properties resulting from the thermonuclear explosion of sub-Chandrasekhar mass WDs in such systems when they detonate a helium layer accumulated from steady burning of hydrogen at the surface. A fraction of CLS are believed to form a subset of the observed luminous supersoft X-ray sources (SSS). Sub-Chandrasekhar explosions from CLS are disfavored in all types of galaxies at redshifts z > 1. On the other hand, CLS where the WD succeeds to grow to the Chandrasekhar mass are more likely found in spiral galaxies, and absent from early-type galaxies. SNe Ia statistics could (if the uncertainties still involved are reduced) help to discriminate among proposed SNe Ia scenarios. The range of variation of the characteristics of SNe Ia in the CLS scenario should be narrower than in symbiotics. The predicted correlation between peak luminosity and expansion velociy of the ejecta in SNe Ia coming from these systems is weak. For CLS, the distinction between the characteristics of SNe Ia respectively arising from sub-Chandrasekhar and from Chandrasekhar-mass explosions should be sharp, since all sub-Chandrasekhar