Light curve studies of nearby Type Ia Supernovae with a Multi-band Stretch method

We create new U, B, V, R and I-band light curve templates of type Ia Supernovae (SNe Ia) and re-analyze 122 nearby (redshift < 0.11) SNe Ia using a new Multi-band Stretch method,'' which is a revised Stretch method (cf. Perlmutter et al. 1997; Goldhaber et al. 2001) extended to five bands. We find (i) our I-band template can fit about 90% of SNe Ia I-band light curves, (ii) relationships between luminosity, colours and stretch factors, (iii) possible sub-groups of SNe Ia, and (iv) the ratio of total to selective extinction R in other galaxies can be consistent with that in the Milky Way under the assumption that SNe Ia have diversity in their intrinsic colour. Based on these results, we discuss how to select subsets of SNe Ia to serve as good distance indicators for cosmology. We find two possibilities: one is to choose BV bluest’’ (-0.14 < (B-V)_{max} <= -0.10) objects and the other is to use only SNe Ia which occur in E or S0 galaxies. Within these subsets, we find the root mean square (r.m.s.) of peak B-band magnitudes is 0.17 mag (``BV bluest’’ sample) and 0.12 mag (E or S0 sample).