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[18.09] On Variations in the Peak Luminosity of Type Ia Supernovae

J.W. Truran, F.X. Timmes, E.F. Brown (Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago)

We explore the idea that the observed variation in the peak luminosities of Type Ia supernovae originates in part from a scatter in metallicity of the main-sequence stars that become white dwarfs. For any explosion model that reaches nuclear statistical equilibrium outside the innermost 0.2\,M_\odot, the mass of ⁵⁶\mathrm{Ni} produced depends linearly on the initial metallicity of the progenitor. Detailed post-processing of W7 models confirms this linear dependence. We calculate that the observed scatter in the initial CNO abundances (from one-third to thrice solar) induces a 25% variation in the mass of ⁵⁶\mathrm{Ni} ejected by Type Ia supernova, sufficient to account for about a 0.2 magnitude variation in the peak V-band luminosity. This scatter in metallicity is present out to the limiting redshifts of current observations (Z < 1). Sedimentation of the ²²\mathrm{Ne} can further reduce the amount of ⁵⁶\mathrm{Ni} produced, making the maximum variation < 50% in the ⁵⁶\mathrm{Ni} mass (0.4 magnitude in V). Higher metallicity systems produce more ⁵⁴\mathrm{Fe} and ⁵⁸\mathrm{Ni}; this may imply that the ⁵⁴\mathrm{Fe}/⁵⁶\mathrm{Fe} abundance ratio has increased over the past ~5\,\mathrm{Gyr}. This work is supported by the Department of Energy under Grant No.~B341495 to the Center for Astrophysical Thermonuclear Flashes and Grant No.~DE-FG02-91ER40606 in Nuclear Physics and Astrophysics at the University of Chicago.

Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.