Carbon Detection in Early-Time Optical Spectra of Type Ia Supernovae

Details Carbon Detection in Early-Time Optical Spectra of Type Ia Supernovae Carbon Detection in Early-Time Optical Spectra of Type Ia Supernovae

2012-02-16

arxiv.org/abs/1202.3788v2

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

20 pages, 10 figures, 4 tables, submitted to MNRAS

Scientific paper

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.

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