Type Ia Supernova Carbon Footprints
R. C. Thomas, G. Aldering, P. Antilogus, C. Aragon, S. Bailey, C., Baltay, S. Bongard, C. Buton, A. Canto, M. Childress, N. Chotard, Y. Copin,, H. K. Fakhouri, E. Gangler, E. Y. Hsiao, M. Kerschhaggl, M. Kowalski, S., Loken, P. Nugent, K. Paech, R. Pain, E. Pecontal, R. Pereira

TL;DR
This study provides evidence of unburned carbon in several Type Ia supernovae, linking carbon signatures to specific light curve properties and analyzing their evolution to understand explosion mechanisms.
Contribution
First detection of unburned carbon in multiple SNe Ia using automated spectral fitting, and analysis of its relation to light curve and ejecta properties.
Findings
Approximately 22% of SNe Ia show photospheric carbon signatures.
Carbon presence correlates with narrower, bluer light curves.
Spectral analysis suggests low volume filling factor of carbon in ejecta.
Abstract
We present convincing evidence of unburned carbon at photospheric velocities in new observations of 5 Type Ia supernovae (SNe Ia) obtained by the Nearby Supernova Factory. These SNe are identified by examining 346 spectra from 124 SNe obtained before +2.5 d relative to maximum. Detections are based on the presence of relatively strong C II 6580 absorption "notches" in multiple spectra of each SN, aided by automated fitting with the SYNAPPS code. Four of the 5 SNe in question are otherwise spectroscopically unremarkable, with ions and ejection velocities typical of SNe Ia, but spectra of the fifth exhibits high-velocity (v > 20,000 km/s) Si II and Ca II features. On the other hand, the light curve properties are preferentially grouped, strongly suggesting a connection between carbon-positivity and broad band light curve/color behavior: Three of the 5 have relatively narrow light curves…
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