Determination of the hubble constant, the intrinsic scatter of luminosities of type Ia supernovae, and evidence for nonstandard dust in other galaxies

A sample of 109 Type Ia supernovae (SNe Ia) with recession velocity less than or similar to 30,000 km s(-1) is compiled from published SN Ia light curves to explore the expansion rate of the local universe. Based on the color parameter Delta C-12 and the decline rate Delta m(15), we found that the average absorption-to-reddening ratios for SN Ia host galaxies are R-UBVI = 4.37 +/- 0.25, 3.33 +/- 0.11, 2.30 +/- 0.11, and 1.18 +/- 0.11, which are systematically lower than the standard values in the Galaxy. We investigated the correlations of the intrinsic luminosity with light-curve decline rate, color index, and SN environmental parameters. In particular, we found that SNe Ia in E/S0 galaxies close to the central region are brighter than those in the outer region, which may suggest a possible metallicity effect on SN luminosity. The dependence of SN luminosity on galactic environment disappears after corrections for the extinction and Delta C-12. The Hubble diagrams constructed using 73 Hubble flow SNe Ia yield a 1 sigma scatter of less than or similar to 0.12 mag in BVI bands and similar to 0.16 mag in U band. The luminosity difference between normal SNe Ia and peculiar objects (including SN 1991bg-like and SN 1991T-like events) has now been reduced to within 0.15 mag via Delta C-12 correction. We use the same precepts to correct the nearby SNe Ia with Cepheid distances and found that the fully corrected absolute magnitudes of SNe Ia are M-B = -19.33 +/- 0.06 and M-V = -19.27 +/- 0.05. We deduced a value for the Hubble constant of H-0 = 72 +/- 6 (total) km s(-1) Mpc(-1).