Comparative direct analysis of type Ia supernova spectra. II. Maximum light

A comparative study of near-maximum-light optical spectra of 24 Type Ia supernovae (SNe Ia) is presented. The spectra are assigned to four groups. Seven core-normal SNe Ia have very similar spectra, except for strong, high-velocity Ca II absorption in SN 2001el. Seven SNe Ia are assigned to a broad-line group, the most extreme of which is SN 1984A. Five SNe Ia, including SN 1991bg, are assigned to a cool group. Five SNe Ia, including SN 1991T, are assigned to a shallow-silicon group. Comparisons with SYNOW synthetic spectra provide a basis for discussion of line identifications and an internally consistent quantification of the maximum-light spectroscopic diversity among SNe Ia. The extent to which SN Ia maximum-light spectra appear to have a continuous distribution of properties, rather than consist of discrete subtypes, is discussed.