The reddening-free decline rate versus luminosity relationship for type Iasupernovae

We develop a method for estimating the host galaxy dust extinction for type Ia supernovae based on an observational coincidence first noted by Lira, w ho 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 s hape. This fact is used to calibrate the dependence of the B-max-V-max and V-max-I-max colors on the light-curve decline rate parameter Delta m(15)(B) , which can, in turn, be used to separately estimate the host galaxy extinc tion. Using these methods to eliminate the effects of reddening, we reexami ne the functional form of the decline rate versus luminosity relationship a nd provide an updated estimate of the Hubble constant of H-o = 63.3 +/- 2.2 (internal) +/- 3.5(external) km s(-1) Mpc(-1).