Prior to the incineration of a white dwarf ( WD ) that makes a Type Ia supernova ( SN Ia ) , the star “ simmers ” for \sim 1000 years 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 ^ { 22 } Ne 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 _ { \odot } \lesssim 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 can not provide for the full observed diversity of events .