The case against the progenitor's carbon-to-oxygen ratio as a source of peak luminosity variations in type Ia supernovae

One of the major challenges for theoretical modeling of type Ia supernova explosions is to explain the diversity of these events and the empirically established correlation between their peak luminosity and light Curve shape. In the framework of the so-called Chandrasekhar mass models, the progenitor's carbon-to-oxygen ratio has been suggested as a principal source of peak luminosity variations due to a variation in the production of radioactive Ni-56 during the explosion. We describe a mechanism resulting from an interplay between nucleosynthesis and turbulent flame evolution which counteracts such ail effect. Based on three-dimensional simulations we argue that it is nearly balanced and only minor differences in the amount of synthesized Ni-56 with varying carbon mass fraction in the progenitor can be expected. Therefore the progenitor's carbon-to-oxygen ratio is unlikely to account for the observed variations in type la supernova luminosity. We discuss possible effects on the calibration of cosmoloeical measurements.