Institute for Advanced Study Astrophysics Seminar - NOTE LOCATION!
On the Source of the Dust Extinction in Type Ia Supernovae
ABSTRACT: Echelle observations can be used as an independent means of probing the dust extinction of SNe Ia. I show that the extinction of the objects where the diffuse interstellar band at 5780 Angstroms is detected is consistent with the visual extinction derived from the supernova colors. This strongly suggests that the dust is predominantly located in the interstellar medium of the host galaxies and not in circumstellar material associated with the progenitor system. However, the echelle spectra also reveal that one quarter of the supernovae display anomalously large Na I column densities in comparison to the amount of dust extinction derived from their colors. Remarkably, all of the cases of unusually strong Na I D absorption correspond to “Blueshifted” profiles in the classification scheme of Sternberg et al. (2011). This coincidence suggests that outflowing circumstellar gas is responsible for at least some of the cases of anomalously large Na I column densities.