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G. H. Marion, P. Höflich (University of Texas), W. D. Vacca (Max-Planck-Institut fuer extraterrestrische Physik), J. C. Wheeler (University of Texas)
We have obtained near infrared (NIR) spectroscopic observations of twelve ``Branch-normal'' Type Ia supernovae (SNe Ia) covering the wavelength region from 0.8-2.5 \mum at epochs from ten days before to eighteen days after maximum light. The NIR is an extremely useful tool to probe the chemical structure in the layers of SNe Ia ejecta. This wavelength region is optimal for examining certain products of the SNe Ia explosion that are blended or obscured in other spectral regions. We identify spectral features from \ion{Mg}{2},\ion{Mn}{2}, \ion{Ca}{2}, \ion{Si}{2}, \ion{Fe}{2}, \ion{Co}{2} and \ion{Ni}{2}, and we find no indications of hydrogen, helium or carbon.
Detailed models for Type Ia supernovae are used to identify the spectral features. The Doppler shifts of absorption lines are measured to obtain expansion velocities for the elements observed. The velocities provide the radial distribution of elements. We use the data to derive upper limits for the amount of unburned matter, to identify the transition regions from explosive carbon to oxygen burning and from partial to complete silicon burning, and to estimate the level of mixing during and after the explosion.
We find that intermediate mass elements synthesized in the outer layers during the explosion appear to remain in distinct layers. The lack of carbon in the spectra suggests that burning during the explosion reaches the outermost layers of the progenitor. We also find that \ion{Mg}{2} velocities exceed 15,000 km s-1 in most SNe Ia which provides an upper limit for the amount of unburned material of \leq 0.1 M\odot. The results of our analysis are consistent with delayed detonation (DD) models of SNe Ia. The data strongly favor models where the entire progenitor, including the outermost layers, undergo burning and that there is no strong mixing of the chemical layers.
The author(s) of this abstract have provided an email address for comments about the abstract: hman@astro.as.utexas.edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.