Spectroscopic Observations and Analysis of the Unusual Type Ia SN 1999ac
Jul, 200540 pages
Published in:
- Astron.J. 130 (2005) 2278-2292
e-Print:
- astro-ph/0507288 [astro-ph]
DOI:
Report number:
- FERMILAB-PUB-05-686-A
Experiments:
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Abstract: (arXiv)
We present optical spectra of the peculiar Type Ia supernova (SN Ia) 1999ac. The data extend from -15 to +42 days with respect to B-band maximum and reveal an event that is unusual in several respects. Prior to B-band maximum, the spectra resemble those of SN 1999aa, a slowly declining event, but possess stronger SiII and CaII signatures (more characteristic of a spectroscopically normal SN). Spectra after B-band maximum appear more normal. The expansion velocities inferred from the Iron lines appear to be lower than average; whereas, the expansion velocity inferred from Calcium H and K are higher than average. The expansion velocities inferred from SiII are among the slowest ever observed, though SN 1999ac is not particularly dim. The analysis of the parameters v_10, R(SiII), dv(SiII)/dt, and d_m15 further underlines the unique characteristics of SN 1999ac. We find convincing evidence of CII 6580 in the day -15 spectrum with ejection velocity v > 16,000 km/s, but this signature disappears by day -9. This rapid evolution at early times highlights the importance of extremely early-time spectroscopy.Note:
- 40 pages, 24 figures, accepted for publication in The Astronomical Journal
- supernovae: general
- supernovae: individual (SN 1999ac)
References(54)
Figures(24)