Abstract
The large luminosities of type II supernovae (SNe) (those with a hydrogen-rich envelope) make this class of objects an interesting distance indicator. Their luminosities can be standardized using the expansion velocity of the photosphere estimated from P-Cygni line profiles of Fe II (Hamuy & Pinto 2002, ApJ, 566, L63). However, one of the problems that hampers their use in distance determinations is the uncertainty in the host-galaxy extinction.
In this work we examine the usefulness of the V - I color measured toward the end of the plateau phase (the optically thick era of the supernova) as a reddening estimator. For this purpose we first assume a standard reddening law (R_V = 3.1) and then we relax this constrain and solve for R[V] by minimizing the dispersion in the Hubble diagram.
>From a set of 30 type II plateau SNe we obtain a dispersion in the Hubble diagram of 0.4 mag when we fix R_V to 3.1, and 0.3 mag when we treat R[V] as a free parameter. In the latter case we find R_V = 1.71+/-0.11, which suggests a significantly different extinction law than the Galactic case.
The calibration of the Hubble diagrams, using Cepheid distances for SN 1999em (Leonard et al. 2002, PASP, 114, 35) and SN 2004dj (Freedman et al. 2001, ApJ, 553, 47), yields a weighted mean of BVI filters for the Hubble constant of 71.3+/-3.4~km s^-1 Mpc^-1 using the second technique for dereddening.
