Title: The Diversity of Type Ia Supernovae in the Intermediate Redshift Universe
Author(s): K. Konishi, N. Yasuda, M. Doi, Y. Ihara and K. Tokita
Abstract:

The cosmological standard candle is a very important tool in estimating the cosmological parameters and their time evolution. Since type Ia supernovae (SNe Ia) are as bright as a galaxy with small dispersion of the maximum brightness, they are one of the most powerful candidates for the standard candle. Recent optical studies have revealed that the maximum brightness is highly correlated with their lightcurve shapes as well as equivalent widths. The understanding of the SN Ia diversity is not only the key for the precise estimation of cosmological parameters but also have some contribution for modeling. Hence many researchers have investigated the diversity of SNe Ia. These works, however, have been restricted to nearby or high-z SNe Ia, and almost no studies have been done with SNe Ia in the intermediate redshift, especially in the rest-frame ultraviolet range.
We conducted the SDSS Supernova Survey which aimed to find SNe Ia at the intermediate redshift (z=0.1-0.4). This Survey have carried out three year observations (2005-2007) using the 2.5m telescope with its five band photometric system. As a spectroscopic follow-up program, we observed spectra of 71 SN Ia candidates with the Subaru/FOCAS in the first two seasons and obtained 58 SN Ia spectra ranging from rest-frame ultraviolet to optical wavelength. We discuss the observed diversity by investigating the time evolution of the velocities and equivalent widths of ultraviolet/optical lines, the correlations among these spectroscopic properties and photometric parameters of lightcurve widths and colors.