Spectroscopic observations and analysis of the unusual Type Ia SN 1999ac

Authors

G. Garavini, Laboratoire de Physique Nucléaire et de Hautes Energies
G. Aldering, Lawrence Berkeley National LaboratoryFollow
A. Amadon, CEA Saclay
R. Amanullah, Stockholms universitetFollow
P. Astier, Stockholms universitet
G. Ballanc, Laboratoire de Physique Nucléaire et de Hautes Energies
G. Blanc, Osservatorio Astronomico di Padova
A. Conley, Lawrence Berkeley National Laboratory
T. Dahlén, Stockholms universitet
S. E. Deustua, American Astronomical Society
R. Ellis, California Institute of Technology
S. Fabbro, Universidade de Lisboa
V. Fadeyev, Lawrence Berkeley National Laboratory
X. Fan, The University of Arizona
G. Folatelli, Stockholms universitet
B. Frye, Lawrence Berkeley National Laboratory
E. L. Gates, University of California, Santa Cruz
R. Gibbons, Vanderbilt University
G. Goldhaber, Lawrence Berkeley National Laboratory
B. Goldman, New Mexico State University
A. Goobar, Stockholms universitet
D. E. Groom, Lawrence Berkeley National Laboratory
J. Haissinski, Laboratoire de l'Accélérateur Linéaire
D. Hardin, Laboratoire de Physique Nucléaire et de Hautes Energies
I. Hook, University of Oxford
D. A. Howell, University of Toronto
S. Kent, Fermi National Accelerator Laboratory
A. G. Kim, Lawrence Berkeley National Laboratory
R. A. Knop, Vanderbilt University
M. Kowalski, Lawrence Berkeley National Laboratory
N. Kuznetsova, Lawrence Berkeley National Laboratory
B. C. Lee, Lawrence Berkeley National Laboratory
C. Lidman, European Southern Observatory Santiago

Document Type

Article

Publication Date

11-1-2005

Abstract

We present optical spectra of the peculiar Type la 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), v̇, and Δm 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. © 2005. The American Astronomical Society. All rights reserved.

Publication Source (Journal or Book title)

Astronomical Journal

First Page

2278

Last Page

2292

Recommended Citation

Garavini, G., Aldering, G., Amadon, A., Amanullah, R., Astier, P., Ballanc, G., Blanc, G., Conley, A., Dahlén, T., Deustua, S., Ellis, R., Fabbro, S., Fadeyev, V., Fan, X., Folatelli, G., Frye, B., Gates, E., Gibbons, R., Goldhaber, G., Goldman, B., Goobar, A., Groom, D., Haissinski, J., Hardin, D., Hook, I., Howell, D., Kent, S., Kim, A., Knop, R., Kowalski, M., Kuznetsova, N., Lee, B., & Lidman, C. (2005). Spectroscopic observations and analysis of the unusual Type Ia SN 1999ac. Astronomical Journal, 130 (5), 2278-2292. https://doi.org/10.1086/444595