Cepheid calibration of Type Ia supernovae and the Hubble constant

We investigate how a different calibration of the Cepheid period-luminosity (PL) relation, taking into account metallicity corrections, affects the absolute magnitude calibration of Type Ia supernovae (SNe Ia) and, in turn, the determination of the Hubble constant H 0 . We use SN Ia light curves from the literature and previously unpublished data to establish the M B -Δm 15 (B) relation, and calibrate the zero point by means of nine SNe Ia with Cepheid-measured distances. This relation is then used to establish the Hubble diagram, and in turn to derive H 0 . In the attempt to correct for the host-galaxy extinction, we find that the data suggest a value for the total to selective absorption ratio of R B = 3.5, which is smaller than the standard value for our own Galaxy of R B = 4.315. Depending on the metallicity correction for the Cepheid PL relation, the value of R B , and SN sample selection criteria, the value of the Hubble constant H 0 takes a value in the range 68-74 km s -1 Mpc -1 , with associated uncertainties of the order of 10 per cent. Unpublished photometry is also presented for 18 SNe of our sample (1991S, 1991T, 1992A, 1992K, 1993H, 1993L, 1994D, 1994M, 1994ae, 1995D, 1995ac, 1995bd, 1996bo, 1997bp, 1997br, 1999aa, 1999dk, 2000cx). These data are the results of a long-standing effort in supernova monitoring at ESO - La Silla and Asiago observatories.