Spectral sequences of Type Ia supernovae. II. Carbon as a diagnostic tool for explosion mechanisms. (arXiv:1902.01904v1 [astro-ph.HE])

Spectral sequences of Type Ia supernovae. II. Carbon as a diagnostic tool for explosion mechanisms. (arXiv:1902.01904v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Heringer_E/0/1/0/all/0/1">E. Heringer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kerkwijk_M/0/1/0/all/0/1">M. H. van Kerkwijk</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sim_S/0/1/0/all/0/1">S. A. Sim</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kerzendorf_W/0/1/0/all/0/1">W. E. Kerzendorf</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Graham_M/0/1/0/all/0/1">Melissa L. Graham</a>

How an otherwise inert carbon-oxygen white dwarf can be made to explode as a
Type Ia supernova remains unknown. A promising test of theoretical models is to
constrain the distribution of material that is left unburned, in particular of
carbon. So far, most investigations used line identification codes to detect
carbon in the ejecta, a method that cannot be readily compared against model
predictions because it requires assumed opacities and temperatures. Here, we
instead use tomographic techniques to investigate the amount of carbon in the
inner layers of SN~2011fe, starting from the previously published tomographic
analysis of Mazzali et al. From the presence of the carbon feature in the
optical at early epochs and its disappearance later on, we derive an average
carbon mass fraction between 0.001 and 0.05 for velocities in the range $13500
lesssim v lesssim 16000 rm{km s^{-1}}$, and an upper limit of 0.005 inside
that region. Based on our models and the assumed density profile, only small
amounts of carbon should be in the neutral state, too little to be responsible
for features seen in near-infrared spectra that were previously identified as
due to neutral carbon; We discuss possible reasons for this discrepancy. We
compare our results against a suite of explosion models, although uncertainties
in both the models and our simulations make it difficult to draw definitive
conclusions.

How an otherwise inert carbon-oxygen white dwarf can be made to explode as a
Type Ia supernova remains unknown. A promising test of theoretical models is to
constrain the distribution of material that is left unburned, in particular of
carbon. So far, most investigations used line identification codes to detect
carbon in the ejecta, a method that cannot be readily compared against model
predictions because it requires assumed opacities and temperatures. Here, we
instead use tomographic techniques to investigate the amount of carbon in the
inner layers of SN~2011fe, starting from the previously published tomographic
analysis of Mazzali et al. From the presence of the carbon feature in the
optical at early epochs and its disappearance later on, we derive an average
carbon mass fraction between 0.001 and 0.05 for velocities in the range $13500
lesssim v lesssim 16000 rm{km s^{-1}}$, and an upper limit of 0.005 inside
that region. Based on our models and the assumed density profile, only small
amounts of carbon should be in the neutral state, too little to be responsible
for features seen in near-infrared spectra that were previously identified as
due to neutral carbon; We discuss possible reasons for this discrepancy. We
compare our results against a suite of explosion models, although uncertainties
in both the models and our simulations make it difficult to draw definitive
conclusions.

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