opposite sign for the dependence of the rate of Type Ia SNe on metallicity. Stars of lower metallicity at a given mass generally produce more massive white dwarfs according to stellar evolution calculations (e.g., @Umeda:1998ij [@Marigo:2007xq; @Meng:2007ni]), which should make it easier for them to reach the Chandrasekhar mass and explode. For example, according to @Marigo:2007xq, a single star with an initial mass of $3\,M_{\odot}$ will leave behind a $\simeq 0.7\,M_{\odot}$ white dwarf when evolved at solar metallicity ($Z_\odot=0.019$), while a star with the same initial mass at much lower metallicity ($Z=0.001$) will leave behind a $>0.8\,M_{\odot}$ white dwarf. Due to the steepness of the stellar initial mass function (IMF), this leads to a larger number of possible SN Ia progenitors. Obviously, producing a Type Ia SN explosion is a more complicated process than just evolving single stars (for example, see the discussion of common envelope phase treatment in @Ruiter:2009dk). However, the observed rate of Type Ia SNe implies that a large fraction ($\sim 2-40$%) of all $3\lesssim M \lesssim 8\,M_{\odot}$ stars will explode as one (e.g., @Maoz:2007xw), which suggests that the binary evolution leading to SN Ia production cannot be “fragile”.

In this paper, we propose that the Type 