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