Program: GN-2009A-Q-24

Late-time ($t \sim 300$~d) observation of near-infrared (NIR) [Fe II] lines has proven to be a very powerful tool for probing the physics of Type~Ia supernova (SN~Ia) explosions. The few available examples have revealed that at least some SNe Ia exhibit a layered ejecta structure which persists down to the innermost regions of the SN envelope, in contradiction to all of the currently popular models of SNe Ia which predict that the innermost regions (at least) should exhibit large-scale turbulent mixing. Thus a key piece of physics is missing from our understanding of these events. NIR spectroscopy of Type~Ia supernovae at these epochs tests the limits of 8~m class telescopes for even the brightest SNe Ia, and so these phenomena remain poorly observed. However, it may be possible to use the strong [Fe II] emission line at 7155 \AA\ to similar effect. Unfortunately this line is usually partly blended with [Ca II] emission which complicates the extraction of the true [Fe II] line profile. We propose to use concurrent NIR and optical spectra of two recent nearby Type~Ia supernovae, both to increase the still anemic data set of late-time SN~Ia spectra, and to act as a pilot study to test whether the dramatic success obtained at great effort in the NIR can be reproduced much more cheaply through optical spectroscopy.