Title: Spectroscopic Diversity of Type Ia Supernovae in SDSS Samples
Author(s): Kouichi Tokita, Mamoru Doi, Naoki Yasuda, Tomoki Morokuma, 
Naohiro Takanashi, Kohki Konishi, YUtaka Ihara, and SDSS collaborations. 
Abstract:
We investigated spectroscopic diversity of type Ia supernovae (SNe Ia) 
using spectra of SNe at intermediate redshift. Especially, we focus 
on diversity of SNe Ia in the short optical wavelength range. 
SN spectra in this wavelength range would provide sensitive probe of 
progenitor metallicity from the point of view of theoretical simulations. 
In addition, understanding of spectroscopic diversity of SN Ia is also 
needed for cosmological studies. 
We used 20 SNe spectra taken with Subaru/FOCAS at around the maximum 
brightness (-5 < t < 5 day) to investigate intrinsic diversity of SNe Ia. 
We made a color-color diagram (U-B vs B-V) by synthesized photometry 
of these spectra. In the U-B vs B-V diagram, there is a clear trend of 
SNe Ia with an intrinsic dispersion distinct from that caused by extinction.
The dispersion become smaller after the corrections for the stretch factor 
and the epoch, but there is still a significant scatter left. 
Therefore, SNe Ia may have diversity in the short optical wavelength 
that the stretch and epoch can not explain. 
In order to discuss remaining diversity, we compared our results with 
theoretical models under various metallicities and density structures 
of ejecta. Moreover, we estimated an effect of the diversity of SNe Ia 
in the short optical wavelength on cosmological studies.  We successfully 
quantified intrinsic diversity of SNe Ia in the short optical wavelength, 
and the dispersion on cosmological studies caused by the diversity.