Signatures of Delayed Detonation, Asymmetry, and Electron Capture in the Mid-Infrared Spectra of Supernovae 2003hv and 2005df

• Published in: The Astrophysical journal Vol. 661; no. 2; pp. 995 - 1012
• Main Authors: Gerardy, Christopher L, Meikle, W. P. S, Kotak, Rubina, Höflich, Peter, Farrah, Duncan, Filippenko, Alexei V, Foley, Ryan J, Lundqvist, Peter, Mattila, Seppo, Pozzo, Monica, Sollerman, Jesper, Van Dyk, Schuyler D, Wheeler, J. Craig
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 01.06.2007; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Electron capture; Asymmetry; Supernovae; Detonations; supemovae: individual (SN 2003hv, SN 2005df); Infrared spectra; supernovae: general
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/516728

We present mid-infrared (5.2-15.2 mu m) spectra of the Type Ia supernovae (SNe Ia) 2003hv and 2005df observed with the Spitzer Space Telescope. These are the first observed mid-infrared spectra of thermonuclear supernovae, and show strong emission from fine-structure lines of Ni, Co, S, and Ar. The detection of Ni emission in SN 2005df 135 days after the explosion provides direct observational evidence of high-density nuclear burning forming a significant amount of stable Ni in a SN Ia. The SN 2005df Ar lines also exhibit a two-pronged emission profile, implying that the Ar emission deviates significantly from spherical symmetry. The spectrum of SN 2003hv also shows signs of asymmetry, exhibiting blueshifted [Co III], which matches the blueshift of [Fe II] lines in nearly coeval near-infrared spectra. Finally, local thermodynamic equilibrium abundance estimates for the yield of radioactive super(56)Ni give M [unk] approximately 0.5 M [unk], for SN 2003hv, but only M [unk] approximately 0.13-0.22 M [unk] for the apparently subluminous SN 2005df, supporting the notion that the luminosity of SNe Ia is primarily a function of the radioactive super(56)Ni yield. The observed emission-line profiles in the SN 2005df spectrum indicate a chemically stratified ejecta structure, which matches the predictions of delayed detonation (DD) models, but is entirely incompatible with current three-dimensional deflagration models. Furthermore, the degree that this layering persists to the innermost regions of the supernova is difficult to explain even in a DD scenario, where the innermost ejecta are still the product of deflagration burning. Thus, while these results are roughly consistent with a delayed detonation, it is clear that a key piece of physics is still missing from our understanding of the earliest phases of SN Ia explosions.