Neutronization during type Ia supernova simmering

Prior to the incineration of a white dwarf (WD) that makes a Type Ia supernova (SN Ia), the star simmers'' for similar to 1000 yr in a convecting, carbon-burning region. We have found that weak interactions during this time increase the neutron excess by an amount that depends on the total quantity of carbon burned prior to the explosion. This contribution is in addition to the metallicity (Z) dependent neutronization through the Ne-22 abundance (as studied by Timmes, Brown, & Truran). The main consequence is that we expect a floor'' to the level of neutronization that dominates over the metallicity contribution when Z/Z(circle dot) less than or similar to 2/3, and it can be important for even larger metallicities if substantial energy is lost to neutrinos via the convective Urca process. This would mask any correlations between SN Ia properties and galactic environments at low metallicities. In addition, we show that recent observations of the dependences of SNe Ia on galactic environments make it clear that metallicity alone cannot provide for the full observed diversity of events.