A two-parameter luminosity correction for Type Ia supernovae

If, in addition to the usual luminosity correction described by the light curve slope parameter b, we introduce a color correction parameter R, then an extraordinarily good fit is realized for all the 29 distant Type Ia supernovae of the recent Calán/Tololo supernova survey. The reduced χ2 found is much lower than can be expected. All of the intrinsic dispersion is thereby removed from the data sample, leaving perfectly standardized candles insofar as one can measure with present techniques. The best-fit solution has a mysteriously low value for R (referred to the B-band) of about 2 and a value of b ≈ 0.5 which is smaller than previously reported without the color correction. These parameters lead, using pre-Hipparcos distances for Cepheid calibrations, to essentially the same value for the Hubble constant. Our preliminary value, subject to further investigation of Cepheid-calibrated supernovae using this same color correction, is H0 = 60± 6 kms−1Mpc−1.