ZERO-POINT OF THE SUPERNOVA HUBBLE DIAGRAM

An empirical calibration is presented for the absolute luminosity of Type I supernovae using the most reliable distance estimates available to host galaxies of observed supernovae in the Virgo Cluster. Several estimates are presented for the absolute magnitude at maximum blue light; the best one, using planetary nebua distances, gives M(B) = -18.5 +/- 0.2, and the others give slightly different values consistent with the errors. When combined with published Hubble diagrams for distant supernovae, this calibration leads to a Hubble constant in the range 75 less-than-or-equal-to H0 less-than-or-equal-to 100 km s-1 Mpc-1.