Constraints on the Progenitors of Type Ia Supernovae and Implications for the Cosmological Equation of State

Abstract

Detailed calculations for the stellar evolution, explosion and light curves have been performed to quantify the influence of the main sequence mass M(MS) and the metallicity of the progenitor on the structure of the exploding WD which are thought to be the progenitors of SNe Ia. In particular,we study the effects of progenitors on the brightness decline relation M(dM_15) which is a corner stone for the use of SNe Ia as cosmological yard-stick.M(MS) has been identified as the decisive factor to change the energetics of the explosion and dominates the variations in the rise-time to decline relation of light curves. M(MS) has little effect on the color index B-V. For similar decline rates dM_15, the flux at maximum brightness relative to the flux on the radioactive tail decreases systematically with M(MS) by about 0.2mag. This change goes along with a reduc- tion of the photospheric expansion velocity $v_{ph}$ by about 2000 km/sec. A change in the central density has the opposite dependency. The metallicity Z affects mainly the intrinsic color index B-V by up to -0.06mag, and it alters the fluxes in the U band and the UV. B-V is critical if extinction corrections are applied. The spread in the fiducial rise-time to decline relation in local SNe Ia restricts the range of main sequence masses to a factor of 2. The upper limit of 1 day for the difference between the local and distance sample support the need for a positive cosmological constant. The size of evolutionary effects are small (dM abou 0.2mag) but are absolutely critical for the reconstruction of the cosmological equation of state.