Standard Spectral Evolutionary Sequence for Type 1a Supernovae

Spectroscopic monitoring of a wide range of supernovae of different types and at different evolutionary stages has been carried out. The observations were taken using the same instrumentation throughout, and the data have been gathered together in the CANARIAN SUPERNOVAE ARCHIVE (CSNA). The data have been used to carry out an extensive study on type Ia supernovae. As a result, we have been able to establish a template spectral sequence. The sequence is extremely useful in, for example, permitting the identification of intrinsically peculiar objects, and it allows more reliable dating in cases in which photometric information is lacking. The homogeneity of type Ia supernovae is unclear because variations of second order have been detected. However, the validity of the template spectral sequence remains unaffected. In addition, a case-by-case study has been carried out on certain supernovae that seem especially appealing: (i) our discovery of the type Ia twin supernovae 1992R and 1992ac; (ii) analysis of the peculiar type Ia supernovae 1991F which supports the existence of a new supernova sub-group. This revised version was published online in July 2006 with corrections to the Cover Date.