ABSTRACT. We develop a method for estimating the host galaxy dust extinction for type Ia supernovae based on an observational coincidence first 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 B_max-V_max and V_max-I_max colors on the light-curve decline rate parameter Δm₁₅(B), which can, in turn, be used to separately estimate the host galaxy extinction. Using these methods to eliminate the effects 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.

Key words: distance scale; supernovae: general

⁷ Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

Print publication: Issue 4 (1999 October)
Received 27 January 1999, accepted for publication 1 July 1999