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Published online by Cambridge University Press: 11 August 2009
Abstract
We explore whether the observed variations in the peak luminosities of Type Ia supernovae originate in part from a scatter in metallicity of the main-sequence stars that become white dwarfs. Previous, numerical, studies have not self-consistently explored metallicities greater than solar. One-dimensional, Chandrasekhar mass models of SNe Ia produce most of their 56Ni in a burn to nuclear statistical equilibrium between the mass shells 0.2 M⊙ and 0.8 M⊙, for which the electron to nucleon ratio Ye is constant during the burn. We show analytically that, under these conditions, charge and mass conservation constrain the mass of 56Ni produced to depend linearly on the original metallicity of the white dwarf progenitor. This effect is most evident at metallicities greater than solar. Detailed post-processing of W7-like models confirms this linear dependence, and our calculations are in agreement with previous self-consistent calculations over the metallicity range common to both calculations. The observed scatter in the metallicity (1/3 Z⊙-3 Z⊙) of the solar neighborhood is enough to induce a 25% variation in the mass of 56Ni ejected by Type Ia supernova and is sufficient to vary the peak V-band brightness by |ΔMV| ≈ 0.2. This scatter in metallicity is present out to the limiting redshifts of current observations (z ≲ 1). Sedimentation of 22Ne can possibly amplify the variation in 56Ni mass to ≲50%. Further numerical studies can determine if other metallicity-induced effects, such as a change in the mass of the 56Ni-producing region, offset or enhance the variation we identify.
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