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Astronomical Journal 130 (2005) 2278-2292
Spectroscopic Observations and Analysis of the Unusual Type Ia SN 1999ac
G. Garavini1, G. Aldering, A. Amadon, R. Amanullah, P. Astier1, C. Balland1, 2, G. Blanc, A. Conley, T. Dahlén, 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. Haissinski3, D. Hardin1, 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. Moniez3, M. Mouchet2, 4, A. Mourão, H. Newberg, S. Nobili1, P.E. Nugent, R. Pain1, O. Perdereau3, S. Perlmutter, R. Quimby, N. Regnault1, J. Rich, G.T. Richards, P. Ruiz-Lapuente, B.E. Schaefer, K. Schahmaneche1, E. Smith, A.L. Spadafora, V. Stanishev, R.C. Thomas, N.A. Walton, L. Wang, W.M. Wood-Vasey
SUPERNOVAE Collaboration(s)

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.
1 :  LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
2 :  APC - UMR 7164 - AstroParticule et Cosmologie
3 :  LAL - Laboratoire de l'Accélérateur Linéaire
4 :  LUTH - Laboratoire Univers et Théories
APC - Cosmologie et Gravitation
Planète et Univers/Astrophysique

Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique/Cosmologie et astrophysique extra-galactique
supernovae: general – supernovae: individual (SN 1999ac)
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