Spectroscopic Observations and Analysis of the Unusual Type Ia SN 1999ac
Abstract
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.
Cite
@article{arxiv.astro-ph/0507288,
title = {Spectroscopic Observations and Analysis of the Unusual Type Ia SN 1999ac},
author = {The Supernova Cosmology Project and : and G. Garavini and G. Aldering and A. Amadon and R. Amanullah and P. Astier and C. Balland and G. Blanc and A. Conley and T. Dahlen and S. E. Deustua and R. Ellis S. Fabbro and V. Fadeyev and X. Fan and G. Folatelli and B. Frye and E. L. Gates and R. Gibbons and G. Goldhaber and B. Goldman and A. Goobar and D. E. Groom and J. Haissinski and D. Hardin and I. Hook and D. A. Howell and S. Kent and A. G. Kim and R. A. Knop and M. Kowalski and N. Kuznetsova and B. C. Lee C. Lidman and J. Mendez and G. J. Miller and M. Moniez and M. Mouchet and A. Mourao and H. Newberg and S. Nobili and P. E. Nugent and R. Pain and O. Perdereau and S. Perlmutter and R. Quimby and N. Regnault and J. Rich and G. T. Richards and P. Ruiz-Lapuente and B. E. Schaefer and K. Schahmaneche and E. Smith and A. L. Spadafora and V. Stanishev and R. C. Thomas and N. A. Walton and L. Wang and W. M. Wood-Vasey},
journal= {arXiv preprint arXiv:astro-ph/0507288},
year = {2012}
}
Comments
40 pages, 24 figures, accepted for publication in The Astronomical Journal