SIMBAD references

A sample of 109 Type Ia supernovae (SNe Ia) with recession velocity ≲30,000 km/s is compiled from published SN Ia light curves to explore the expansion rate of the local universe. Based on the color parameter ΔC₁₂and the decline rate Δm₁₅, 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 ΔC₁₂. The Hubble diagrams constructed using 73 Hubble flow SNe Ia yield a 1 σ scatter of ≲0.12 mag in BVI bands and ∼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 ΔC₁₂correction. 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 H₀=72±6 (total) km/s/Mpc.