2005/07/12 by The Supernova Cosmology Project, :, G. Garavini +76
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Event (particle physics) #Gamma-ray bursts and supernovae #Physics #Pulsars and Gravitational Waves Research #Spectral line #Supernova #astro-ph
paper · pdf · doi:10.1086/444595
published as Astron.J.130:2278-2292,2005 · 40 pages, 24 figures, accepted for publication in The Astronomical Journal
arxiv created 2005/07/12 · openalex publication_date 2005/10/26 · arxiv updated 2012/08/27 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
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 Si II and Ca II signatures (more characteristic of a spectroscopically normal SN). Spectra after the 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 Si II are among the slowest ever observed, although SN 1999ac is not particularly dim. The analysis of the parameters v 10 (Si II), R (Si II), , and Δ m 15 further underlines the unique characteristics of SN 1999ac. We find convincing evidence of C II λ6580 in the day -15 spectrum with ejection velocity v > 16,000 km s -1 , but this signature disappears by day -9. This rapid evolution at early times highlights the importance of extremely early-time spectroscopy.