Low Carbon Abundance in Type Ia Supernovae
Abstract
We investigate the quantity and composition of unburned material in the outer layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr, and 2004bw. Pristine matter from a white dwarf progenitor is expected to be a mixture of oxygen and carbon in approximately equal abundance. Using near-infrared (NIR, 0.7-2.5 μm) spectra, we find that oxygen is abundant, while carbon is severely depleted with low upper limits in the outer third of the ejected mass. Strong features from the O I line at λrest=0.7773 μm are observed through a wide range of expansion velocities ~(9-18)×103 km s-1. This large velocity domain corresponds to a physical region of the supernova with a large radial depth. We show that the ionization of C and O will be substantially the same in this region. C I lines in the NIR are expected to be 7-50 times stronger than those from O I, but there is only marginal evidence of C I in the spectra and none of C II. We deduce that for these three normal SNe Ia, oxygen is more abundant than carbon by factors of 102-103. Mg II is also detected in a velocity range similar to that of O I. The presence of O and Mg combined with the absence of C indicates that for these SNe Ia, nuclear burning has reached all but the extreme outer layers; any unburned material must have expansion velocities greater than 18×103 km s-1. This result favors deflagration to detonation transition (DD) models over pure deflagration models for SNe Ia.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2006
- DOI:
- 10.1086/502712
- arXiv:
- arXiv:astro-ph/0601614
- Bibcode:
- 2006ApJ...645.1392M
- Keywords:
-
- Infrared: Stars;
- Line: Formation;
- Line: Identification;
- Stars: Supernovae: General;
- Astrophysics
- E-Print:
- accepted for publication in ApJ