Jeffrey M. Silverman, Alexei V. Filippenko
While O is often seen in spectra of Type Ia supernovae (SNe Ia) as both
unburned fuel and a product of C burning, C is only occasionally seen at the
earliest times, and it represents the most direct way of investigating
primordial white dwarf material and its relation to SN Ia explosion scenarios
and mechanisms. In this paper, we search for C absorption features in 188
optical spectra of 144 low-redshift (z < 0.1) SNe Ia with ages <3.6 d after
maximum brightness. These data were obtained as part of the Berkeley SN Ia
Program (BSNIP; Silverman et al. 2012a,b, submitted) and represent the largest
spectral dataset in which C has ever been searched. We find that ~11 per cent
of the SNe studied show definite C absorption features while ~25 per cent show
some evidence for C II in their spectra. Also, if one obtains a spectrum at t <
-5 d, then there is a better than 30 per cent chance of detecting a distinct
absorption feature from C II. SNe Ia that show C are found to resemble those
without C in many respects, but objects with C tend to have bluer optical
colours than those without. The typical expansion velocity of the C II 6580
Ang. feature is measured to be 12,000-13,000 km/s, and the ratio of the C II
6580 Ang. to Si II 6355 Ang. velocities is remarkably constant with time and
among different objects with a median value of ~1.05. While the
pseudo-equivalent widths (pEWs) of the C II 6580 Ang. and C II 7234 Ang.
features are found mostly to decrease with time, we see evidence of a
significant increase in pEW between ~12 and 11 d before maximum brightness,
which is actually predicted by some theoretical models. The range of pEWs
measured from the BSNIP data implies a range of C mass in SN Ia ejecta of about
(2-30) x 10^{-3} M_Sun.
View original:
http://arxiv.org/abs/1202.3788
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