MAXIMUM BRIGHTNESS AND POSTMAXIMUM DECLINE OF LIGHT CURVES OF TYPE SUPERNOVAE IA - A COMPARISON OF THEORY AND OBSERVATIONS

We compare the observed correlations between the maximum brightness, p ostmaximum decline rate, and color at maximum light of Type Ia superno vae (SNs Ia) with model predictions. The observations are based on a t otal of 40 SNs Ia, including 29 SN of the Calan Tololo Supernova Searc h and 11 local SNs which cover a range of approximate to 2 mag in the absolute visual brightness. The observed correlations are not tight, o ne dimensional relations. Supernovae with the same postmaximum decline or the same color have a spread in visual magnitude of approximate to 0.7 mag. The dispersion in the color-magnitude relation may result fr om uncertainties in the distance determinations or the interstellar re ddening within the host galaxy. The dispersion in the decline rate-mag nitude relation suggests that an intrinsic spread in the supernova pro perties exists that cannot be accounted for by any single relation bet ween visual brightness and postmaximum decline.Theoretical correlation s are derived from a grid of models which encompasses delayed detonati ons, pulsating delayed detonations, the merging scenario, and helium d etonations. We find that the observed correlations can be understood i n terms of explosions of Chandrasekhar mass white dwarfs. Our models s how an intrinsic spread in the relations of about 0.5 mag in the maxim um brightness and approximate to 0.1 mag in the B-V color. Our study p rovides strong evidence against the mechanism of helium detonation for subluminous, red SNs Ia.