UC Berkeley

An interesting way to calibrate the absolute magnitudes of remote Type Ia supernovae (SNe Ia) that are well out in the Hubble flow, and thus determine the value of the Hubble constant, H_0, has been introduced by van den Bergh. His approach relies on calculations of the peak absolute magnitudes and broad--band colors for SN Ia explosion models. It does not require any corrections for extinction by interstellar dust, and no SNe Ia are excluded on grounds of peculiarity. Within the last few years distances have been determined to the parent galaxies of six SNe Ia by means of Cepheid variables. Cepheid--based distances also have become available for three other SNe Ia if one is willing to use the distance to a galaxy in the same group in lieu of the distance to the parent galaxy itself. Here we determine the value of H_0 in a way that is analogous to that of van den Bergh, but now using Cepheid--based distances instead of calculated light curves. We obtain H_0 = 55 km/s/Mpc. This value, with Lambda=0 and Omega=1, corresponds to a cosmic expansion time of 12 Gyr, which is consistent with several recent determinations of the ages of globular clusters.