Spectral diversity of Type Ia Supernovae

We use published spectroscopic and photometric data for eight Type Ia supernovae (SNe Ia) to construct a dispersion spectrum for this class of object, showing their diversity over the wavelength range 3700-7100A. We find that the B and V bands are the spectral regions with the least dispersion, while the U band below 4100A is more diverse. Some spectral features such as the Si line at 6150A are also highly diverse. We then construct two objective measures of `peculiarity' by (i) using the deviation of individual objects from the average SN Ia spectrum compared to the typical dispersion and (ii) applying principal component analysis. We demonstrate these methods on several SNe Ia that have previously been classified as peculiar.