AAS 199th meeting, Washington, DC, January 2002
Session 84. Supernovae Surveys
Display, Wednesday, January 9, 2002, 9:20am-6:30pm, Monroe/Lincoln

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[84.07] Near-Infrared Spectra of Supernovae

C. L. Gerardy, R. A. Fesen (Dartmouth College), P. Hoflich (University of Texas, Austin), K Nomoto (University of Tokyo), P. M. Garnavich (University of Notre Dame), S. Jha, P. M. Challis, R. P. Kirshner (Harvard-Smithsonian Center for Astrophysics), J. C. Wheeler (University of Texas, Austin), S. Sakai (UCLA)

We present results from a survey of the near-infrared properties of all types of supernovae. Near-infrared spectra of the subluminous Type Ia SN 1999by taken 5 days before to two weeks after maximum light have been analysed using self-consistent SN Ia explosion models. The data generally agree with 1D delayed-detonation models, indicate a near Chandrasekhar-mass WD progenitor, and show low yield of iron-peak elements confined to the innermost layers of the ejecta. This puts strong constraints on the mixing of large iron blobs into the outer layers due to Rayleigh-Taylor instabilities during the deflagration phase.

NIR spectra of Type IIP SNe are relatively line-free during the plateau phase, showing largely hydrogen emission with only a handful of other lines, mostly in the 1-1.2 micron region. After the plateau phase, Type IIP spectra become much richer, showing many overlapping emission features throughout the near-infrared. It appears that CO emission is a common feature of core-collapse supernovae, as several detections of first overtone CO emission near 2.3 microns have been made, including SN 1998S (IIn), SN 1999em, SN 1999gi (IIP) and SN 2000ew (Ic).

Finally, we find that Type IIn supernovae often exhibit extraordinary infrared excesses at late times. This is probably thermal emission from hot dust, most likely in the dense circumstellar gas surrounding the progenitor star. The infrared luminosity can reach 1041-42 erg s-1, and can last for several years. A possible scenario is that the dust emission is an ``infrared echo'' powered not by the flash of the SN explosion, but rather by UV/X-ray emission from the strong shock interaction with the dense circumstellar material.

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