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For refcode 1997MNRAS.290..663B:
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Copyright by Royal Astronomical Society. 1997MNRAS.290..663B Infrared and optical spectroscopy of Type Ia supernovae in the nebular phase E. J. C. Bowers, W. P. S. Meikle, T. R. Geballe, N. A. Walton, P. A. Pinto, V. S. Dhillon, S. B. Howell and M. K. Harrop-Allin Accepted 1997 June 12. Received 1997 June 2; in original form 1997 March 20 ABSTRACT We present near-infrared (NIR) spectra for Type Ia supernovae at epochs of 13 to 338 d after maximum blue light. Some contemporary optical spectra are also shown. All the NIR spectra exhibit considerable structure throughout the J, H and K bands. In particular, they exhibit a flux `deficit' in the J band which persists as late as 175d. This is responsible for the well-known red J - H colour. To identify the emission features and test the ^56^Ni hypothesis for the explosion and subsequent light curve, we compare the NIR and optical nebular-phase data with a simple non-LTE nebular spectral model. We find that many of the spectral features are due to iron-group elements, and that the J-band deficit is due to a lack of emission lines from species that dominate the rest of the IR/optical spectrum. Nevertheless, some emission is unaccounted for, possibly due to inaccuracies in the cobalt atomic data. For some supernovae, blueshifts of 1000-3000 km s^-1^ are seen in infrared and optical features at 3 months. We suggest that this is due to clumping in the ejecta. The evolution of the cobalt/iron mass ratio indicates that ^56^Co-decay dominates the abundances of these elements. The absolute masses of iron-group elements which we derive support the basic thermonuclear explosion scenario for Type Ia supernovae. A core-collapse origin is less consistent with our data. Key words: stars: general - supernovae: general - infrared: stars.
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