Ultraviolet Line Identifications and Spectral Formation Near Max Light in Type Ia Supernova 2011fe.

We present ultraviolet line identifications of near maximum-light Hubble Space Telescope observations of SN 2011fe using synthetic spectra generated from both SYNOW and 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 SNe Ia 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 of its UV spectra shows the power of UV spectra in discriminating between different metallicities and progenitor scenarios of SNe Ia, due to the fact that the UV probes the outermost layers of the SN Ia, which are most sensitive to metallicity and progenitor variations. [ABSTRACT FROM AUTHOR]