Ultraviolet Line Identifications and Spectral Formation Near Max-Light in Type Ia Supernovae 2011fe

TL;DR

This study analyzes ultraviolet spectra of SN 2011fe near maximum light, identifying key spectral lines, comparing observations with models, and highlighting the importance of UV data in understanding supernova progenitors and metallicity effects.

Contribution

First identification of C IV and Si IV lines in a supernova spectrum; demonstrates the effectiveness of classical delayed detonation models in reproducing UV flux; emphasizes UV spectra's role in probing supernova outer layers.

Findings

UV spectra dominated by Fe, Co, Ni blends

Classical delayed detonation models match UV flux levels

UV features sensitive to metallicity and progenitor variations

Abstract

We present ultraviolet line identifications of near maximum-light HST observations of SN 2011fe using synthetic spectra generated from both SYNOW and $\texttt{PHOENIX}$. We find the spectrum to be dominated by blends of iron group elements Fe, Co, and Ni (as expected due to heavy line blanketing by these elements in the UV) and for the first time identify lines from C IV and Si IV in a supernova spectrum. We also find that classical delayed detonation models of Type Ia supernovae are able to accurately reproduce the flux levels of SN 2011fe in the UV. Further analysis reveals that photionization edges play an important role in feature formation in the far-UV, and that temperature variations in the outer layers of the ejecta significantly alter the Fe III/Fe II ratio producing large flux changes in the far-UV and velocity shifts in mid-UV features. SN 2011fe is the best observed core-normal SNe Ia, therefore analysis its of UV spectra shows the power of UV spectra in discriminating between different metalicities and progenitor scenarios of Type Ia supernovae, due to the fact that the UV probes the outermost layers of the Type Ia supernova, which are most sensitive to metalicity and progenitor variations.