Influence of the stellar population on Type Ia supernovae:: Consequences for the determination of Ω

The influence of the metallicity on 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 M-MS of 7 M. 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 that 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 supernova. 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 Population I to Population II causes a change in the zero point of the maximum brightness/decline relation by about 0.1 mag and a change in the rise time by about 1 day. Combined with previous studies, the offset in the maximum brightness/decline Delta M approximate to 0.1 Delta t, where Delta t is the change of the rise time in days. Systematic effects of the size discussed here may well make the results from the SNe Ia searches consistent with a universe with Omega(M) = 0.2 and Omega(Lambda) = 0 but hardly will change the conclusion that we live in a universe with low Omega(M). Variations of the expected size may prove to be critical if, in the future, SNe Ia are used to measure large-scale scalar fields because Z may show large local variations. Evolutionary effects will not change substantially the counting rates for SNe Ia even at very large redshifts. Evolutionary effects may be of the same order as the brightness changes related to cosmological parameters, but we have shown ways how the effects of evolution can be detected.