METALLICITY AS A SOURCE OF DISPERSION IN THE SNIa BOLOMETRIC LIGHT CURVE LUMINOSITY-WIDTH RELATIONSHIP

The recognition that the metallicity of Type Ia supernova (SNIa) progenitors might bias their use for cosmological applications has led to an increasing interest in its role in shaping SNIa light curves. We explore the sensitivity of the synthesized mass of 56 Ni, M ( 56 Ni), to the progenitor metallicity starting from pre-main-sequence models with masses M 0 = 2–7 M ☉ and metallicities Z = 10 −5 –0.10. The interplay between convective mixing and carbon burning during the simmering phase eventually raises the neutron excess, η, and leads to a smaller 56 Ni yield, but does not change substantially the dependence of M ( 56 Ni) on Z . Uncertain attributes of the progenitor white dwarf, like the central density, have a minor effect on M ( 56 Ni). Our main results are: (1) a sizeable amount of 56 Ni is synthesized during incomplete Si-burning, which leads to a stronger dependence of M ( 56 Ni) on Z than obtained by assuming that 56 Ni is produced in material that burns fully to nuclear statistical equilibrium; (2) in one-dimensional delayed detonation simulations a composition dependence of the deflagration-to-detonation transition (DDT) density gives a nonlinear relationship between M ( 56 Ni) and Z and predicts a luminosity larger than previously thought at low metallicities (however, the progenitor metallicity alone cannot explain the whole observational scatter of SNIa luminosities); and (3) an accurate measurement of the slope of the Hubble residuals versus metallicity for a large enough data set of SNIa might give clues to the physics of DDT in thermonuclear explosions.