The diversity of type Ia supernovae

The photometric and spectroscopic properties of 26 well observed Type Ia Supernovae (SNe Ia) were analyzed with the aim to explore SN la diversity. The sample includes (Branch-) normal SNe as well as extreme events like SNe 1991T and 1991bg. A statistical treatment reveals the existence of three different groups. The first group (FAINT) consists of faint SNe la similar to SN 1991bg, with low expansion velocities and rapid evolution of Sill velocity. A second group consists of '' normal '' SNe la, also with high temporal velocity gradient (HVG), but with brighter mean absolute magnitude < M-B >= -19.3 and higher expansion velocities than the FAINT SNe. The third group includes both '' normal '' and SN 1991T-like SNe la: these SNe populate a narrow strip in the Sill velocity evolution plot, with a small velocity gradient (LVG), but have absolute magnitudes similar to HVGs.