Comparative Direct Analysis of Type Ia Supernova Spectra. III. Premaximum

TL;DR

This study compares premaximum spectra of 21 Type Ia supernovae, revealing consistent spectral features across groups and discussing implications for supernova explosion models and ejecta composition.

Contribution

It provides a detailed comparative analysis of premaximum spectra of SNe Ia, confirming spectral group characteristics and evaluating synthetic spectral models.

Findings

Spectral features largely match synthetic models

Presence of high-velocity features and carbon clumps discussed

Spectra support existing supernova explosion theories

Abstract

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 (core-normal, 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.