J un 2 00 7 Comparative Direct Analysis of Type Ia Supernova Spectra . III

A comparative study of spectra of 21 Type Ia supernovae (SNe Ia) obtained about one week before maximum light, and 8 spectra obtained 11 or more days before maximum, is presented. To a large extent the premaximum spectra exhibit the defining characteristics of the four groups defined in Paper II (corenormal, broad–line, cool, and shallow–silicon). Comparisons with SYNOW synthetic spectra show that all strong features and most weak ones can be accounted for in a plausible way. The issues of detached high–velocity features, the possible ubiquity of carbon clumps, the maximum detectable ejecta velocities, and the possibility of blueshifted emission–line peaks are discussed. Subject headings: supernovae: general