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28 March 2024
 
  » arxiv » astro-ph/0507288

 Article overview


Spectroscopic Observations and Analysis of the Unusual Type Ia SN 1999ac
The Supernova Cosmology Project: G. Garavini ; G. Aldering ; A. Amadon ; R. Amanullah ; P. Astier ; C. Balland ; G. Blanc ; A. Conley ; T. Dahlen ; S. E. Deustua ; R. Ellis S. Fabbro ; V. Fadeyev ; X. Fan ; G. Folatelli ; B. Frye ; E. L. Gates ; R. Gibbons ; G. Goldhaber ; B. Goldman ; A. Goobar ; D. E. Groom ; J. Haissinski ; D. Hardin ; I. Hook ; D. A. Howell ; S. Kent ; A. G. Kim ; R. A. Knop ; M. Kowalski ; N. Kuznetsova ; B. C. Lee C. Lidman ; J. Mendez ; G. J. Miller ; M. Moniez ; M. Mouchet ; A. Mourao ; H. Newberg ; S. Nobili ; P. E. Nugent ; R. Pain ; O. Perdereau ; S. Perlmutter ; R. Quimby ; N. Regnault ; J. Rich ; G. T. Richards ; P. Ruiz-Lapuente ; B. E. Schaefer ; K. Schahmaneche ; E. Smith ; A. L. Spadafora ; V. Stanishev ; R. C. Thomas ; N. A. Walton ; L. Wang ; W. M. Wood-Vasey ;
Date 12 Jul 2005
Subject astro-ph
AbstractWe 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.
Source arXiv, astro-ph/0507288
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