Secondary parameters of type Ia supernova light curves

Abstract

High-quality observations of B and V light curves obtained at Las Campanas Observatory for local Type Ia Supernovae (SNe Ia) show clear evidence that SNe Ia with the same brightness decline or stretch may have systematic and independent deviations at times t 5 days before and at times t 30 days after maximum light. This suggests the existence of two independent secondary parameters that control the shape of SN Ia light curves in addition to the primary light curve parameter, stretch s or Δm15. The secondary parameters may reflect two independent physical effects caused by variations in the initial carbon-to-oxygen (C/O) profile in the progenitor and the initial central density ρc in a carbon–oxygen white dwarf exploding as an SN Ia. Theoretical light curves of delayed detonation SN Ia models with varying progenitor masses on the main sequence, varying accretion rates, and varying primordial metallicity reproduce two morphologically different and independent types of variations in observed visual light curves. These calculations predict small variations of ≈0.05 mag in the absolute brightness of SNe Ia which are correlated with the variations of progenitor mass on the main-sequence MMS, which changes the C/O profile, and ρc, which depends on the accretion rate. Such variations in real supernovae will induce systematic errors in SN Ia calibration at high redshifts. A physically motivated three-parameter, s, C/O, ρc, template for SNe Ia light curves might take these variations into account. Comparison between the theoretical predictions and the observational results agree qualitatively; however, the observations show variations between the B and V light curves that are not expected from the modeling and may indicate limitations in the details of the theoretical models.