THE REDDENING-FREE DECLINE RATE VERSUS LUMINOSITY RELATIONSHIP FOR TYPE Ia SUPERNOVAE

Abstract

We develop a method for estimating the host galaxy dust extinction for type Ia supernovae based on an observational coincidence Ðrst noted by Lira, who found that the B[V evolution during the period from 30 to 90 days after V maximum is remarkably similar for all events, regardless of light-curve shape. This fact is used to calibrate the dependence of the Bmax[Vmax and Vmax[Imax colors on the light-curve decline rate parameter *m15 which can, in turn, be used to separately estimate the host galaxy extinc- (B), tion. Using these methods to eliminate the e ects of reddening, we reexamine the functional form of the decline rate versus luminosity relationship and provide an updated estimate of the Hubble constant of H0\63.3^2.2(internal)^3.5(external) km s~1 Mpc~1.