Spectroscopic Observations and Analysis of the Unusual Type Ia SN1999ac
The authors 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 Si II and Ca II 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 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 Si II are among the slowest ever observed, though SN 1999ac is not particularly dim. The analysis of the parameters v{sub 10}(Si II), R(Si II), v, and {Delta}m{sub 15} further underlines the unique characteristics of SN 1999ac. They find convincing evidence of C II {lambda}6580 in the day -15 spectrum with ejection velocity v > 16,000 km s{sup -1}, but this signature disappears by day -9. This rapid evolution at early times highlights the importance of extremely early-time spectroscopy.
- Research Organization:
- COLLABORATION - U. ofParis
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 893063
- Report Number(s):
- LBNL-58301; R&D Project: PSUOPS; BnR: KA1301020; TRN: US0605922
- Journal Information:
- The Astronomical Journal, Vol. 130, Issue 4; Related Information: Journal Publication Date: 10/2005
- Country of Publication:
- United States
- Language:
- English
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