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 quantified in two ways, and assigned to four groups. Seven "core-normal" SNe Ia have very similar spectra, except for strong high-velocity CaII 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 consisting of discrete subtypes, is discussed. 
David Branch, Leeann Chau Dang, Nicholas Hall, Wesley Ketchum, Mercy   Melakayil, Jerod Parrent, M. A. Troxel, D. Casebeer, ...