SUPERNOVA ABSOLUTE-MAGNITUDE DISTRIBUTIONS

The Asiago Supernova Catalogue and the Nearby Galaxies Catalog are used to study the absolute-magnitude distributions of supernovae. SNe Ia that appear to be subluminous are in highly inclined disk galaxies, which implies that the apparent dispersion in SN Ia absolute magnitudes is dominated by interstellar extinction in the parent galaxies, and thus that SNe Ia are good intrinsic standard candles (σ < 0.4 mag). An upper limit to the difference between SNe Ib and SNe Ia in the B band is 1.87 mag, but the bolometric difference is smaller. Due to a large intrinsic range in peak absolute magnitude (≈ 6 mag) the observed sample of SNe II is severely influenced by selection effects; intrinsically faint SNe II (MB ≳ -17 for H0 = 75 km s-1 Mpc-1) are much more common than intrinsically bright ones.