SIMBAD references

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 H₀. We use SN Ia light curves from the literature and previously unpublished data to establish the M_B-Δm₁₅(B) relation, and calibrate the zero point by means of nine SNe Ia with Cepheid-measured distances.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 H₀. 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 H₀takes a value in the range 68-74 km/s/Mpc, 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Unpublished photometry is also presented for 18 SNe of our sample (1991S, 1991T, 1992A, 1992K, 1993H, 1993L, 1994D, 1994M, 1994ae, 1995D, 1995ac, 1995bd, 1996bo, 1997bp,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.