Cepheid calibration of type Ia Supernovae and the Hubble constant
Abstract
We investigate how a different calibration of the Cepheid Period-Luminosity (PL) relation taking into account the metallicity corrections, affects the absolute magnitude calibration of Supernovae (SNe) Ia and, in turn, the determination of the Hubble constant H0. We exploit SN Ia light curves from literature and previously unpublished data, to build the MB -- Delta m15(B) relation and we calibrate the zero point by means of 9 type Ia SNe with Cepheid measured distances. This relation was then used to build the Hubble diagram and in turn to derive H0. In the attempt to correct for the host galaxy extinction, we found that the data seems to suggest a value for the total to selective absorption ratio, RB=3.5, which is smaller than the standard value for our own Galaxy RB=4.315. Depending on different metallicity corrections for the Cepheids P-L relation, values of RB and SN sample selection criteria, we found that the values of the Hubble constant H0 is in the range 68--74 km s-1 Mpc-1, with associated uncertainties of the order of 10%. Unpublished photometry is also presented for 18 SNe of our sample (1991S, 1991T, 1992A, 1992K, 1993H, 1993L, 1994D, 1994M, 1994ae, 1995D, 1995ac, 1995bd, 1996bo, 1997bp,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), which are the results of a long standing effort for supernova monitoring at ESO - La Silla and Asiago Observatories.
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