Influence of the Stellar Population on Type Ia Supernovae: Consequences for the Determination of Omega

Abstract

The influence of the metallicity at the main sequence on the chemical structure of the exploding white dwarf, the nucleosynthesis during the explosion and the light curves of an individual Type Ia supernovae have been studied. Detailed calculations of the stellar evolution, the explosion, and light curves of delayed detonation models are presented. Detailed stellar evolution calculations with a main sequence mass of 7 M_o have been performed to test the influence of the metallicity Z on the structure of the progenitor. A change of Z influences the central helium burning and, consequently, the size of the C/O core which becomes a C/O white dwarf and its C/O ratio. Subsequently, the white dwarf may grow to the Chandrasekhar mass and explode as a Type Ia supernovae. Consequently, the C/O structure of the exploding white dwarf depends on Z. Since C and O are the fuel for the thermonuclear explosion, Z indirectly changes the energetics of the explosion. In our example, changing Z from Pop I to Pop II causes a change in the zero point of the maximum brightness/decline relation by about $0.1^m$ and a change in the rise time by about 1 day. Combined with previous studies, We provide a relation between a change of the rise time in SNeIa and the off-set in the brightness/decline relation. We find that dM = dt where dM is the offset in the relation and dt is the change of the rise time in days. This relation provides a way to detect and test for evolutionary effects, and to estimate the possible consequences for the determination of the cosmological constant. However, due to uncertainties in the time evolution of the properties of the progenitors, we cannot predict whether evolution becomes important at z=0.5, 1 or 2. This question has to be answered by observations.