Introduction

The assumption commonly made is that Supernovae of Type Ia (SN Ia) are the result of thermonuclear runaways (TNR) in the cores of carbon-oxygen white dwarfs (WD) which are members of binary systems and have accreted material from a companion until their masses exceed the Chandrasekhar Limit (Leibundgut 2000, 2001). However, the binary star systems that end in this explosion are not yet known although there have been numerous proposals. Nevertheless, the importance of SN Ia, both to our understanding of the evolution of the Universe and to the formation of iron in the Galaxy, demands that we determine the progenitors of these explosions.

Originally proposed by Whelan and Iben (1973), virtually every type of close binary which contains a WD has been suggested at one time or another. However, based purely on observational concerns, most of the systems that have been proposed cannot be the progenitors (Starrfield 2003). For example, one of the first suggestions was a classical nova system (CN), but the amount of core material ejected during the outburst implies strongly that the WD is losing mass as a result of the outburst (Gehrz et al. 1998). Other suggestions such as Symbiotic Novae (T CrB or RS Oph, for example) can probably be ruled out.because there is too much hydrogen present in the system (the explosion takes place inside the outer layers of a red giant) and the defining characteristic of a SN Ia outburst is the absence of hydrogen in the spectrum (Filippenko 1997).