Benjamin J. Shappee, K. Z. Stanek, R. W. Pogge, P. M. Garnavich
A generic prediction of the single-degenerate model for Type Ia supernovae (SNe Ia) is that a significant amount of material will be stripped from the donor star (~0.5 M_sol for a giant donor and ~0.15 M_sol for a main sequence donor) by the supernova ejecta. This material, excited by gamma-rays from radioactive decay, would then produce relatively narrow (<1000 km s^-1) emission features observable once the supernova enters the nebular phase. Such emission has never been detected, which already provides strong constraints on Type Ia progenitor models. In this Letter we report the deepest limit yet on the presence of H alpha emission originating from the stripped hydrogen in the nebular spectrum of a Type Ia supernova obtained using a high signal-to-noise spectrum of the nearby normal SN Ia 2011fe 274 days after B-band maximum light with the Large Binocular Telescope's Multi-Object Double Spectrograph. We put a conservative upper limit on the H alpha flux of 3.14x10^-17 erg/s/cm^2, which corresponds to a luminosity of 1.57x10^35 erg/s. Assuming the models of Mattila et al. (2005) and the methods of Leonard (2007), this translates into an upper limit of <0.001 M_sol of stripped material, which is an order of magnitude stronger than previous limits by Leonard (2007). SN 2011fe was a typical Type Ia supernova, special only in its proximity, and we argue that lack of hydrogen emission in its nebular spectrum adds yet another strong constraint on the single degenerate class of models for SNe Ia.
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http://arxiv.org/abs/1210.3027
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