2006MNRAS.369L..19M

A variation of the relative content of (⁵⁴Fe+⁵⁸Ni) versus ⁵⁶Ni may be responsible for the observed scatter of Type Ia supernovae (SNe Ia) about a mean relation between their intrinsic brightness and the shape of their light curve. Synthetic light curves are computed from parametrized Chandrasekhar-mass explosion models of constant kinetic energy, where the ejecta are divided into an inner nuclear statistical equilibrium (NSE) zone, composed of (⁵⁴Fe+⁵⁸Ni) inside and ⁵⁶Ni outside, an outer zone with intermediate-mass elements, and a CO zone. Both the size of the NSE zone and the fraction of (⁵⁴Fe+⁵⁸Ni) versus ⁵⁶Ni are varied systematically. Models with the same original NSE content but different (⁵⁴Fe+⁵⁸Ni)/⁵⁶Ni ratios reach different peak brightness but have similar light curve shapes. Synthetic spectra indicate that the V-band decline rate is not affected by the (⁵⁴Fe+⁵⁸Ni)/⁵⁶Ni ratio. While the ⁵⁶Ni mass and the total NSE mass are the dominant parameters that determine the peak luminosity and the shape of the light curve, respectively, a variation in the (⁵⁴Fe+⁵⁸Ni)/⁵⁶Ni ratio, which may depend on the metallicity of the progenitor is likely to account for a significant part of the observed scatter of local SNe Ia about the mean brightness-decline rate relation.