G. H. "Howie" Marion, Jozsef Vinko, J. Craig Wheeler, Ryan J. Foley, Eric Y. Hsiao, Peter J. Brown, Peter Challis, Alexei V. Filippenko, Peter Garnavich, Robert P. Kirshner, Wayne B. Landsman, Jerod T. Parrent, Tyler A. Pritchard, Peter W. A. Roming, Jeffrey M. Silverman, Xiaofeng Wang
We report measurements and analysis of high-velocity (> 20,000 km/s) and photospheric absorption features in a sequence of spectra of SN Ia 2009ig obtained between -14d and +13d with respect to the time of B-band maximum light. We identify lines of Si II, Si III, S II, Ca II and Fe II that produce simultaneous high-velocity (HV) and photospheric velocity (PS) components from -12d to -5d. SN 2009ig is unusual in the number of lines with detectable HV features in its spectra but the light-curve parameters, M_B = -19.46 mag and the Delta m15(B) = 0.90 mag, correspond to a slightly overluminous but unexceptional SN Ia. The velocity of 13,400 km/s for Si II 6355 at the time of B-max is above "normal" for SN Ia but not unusual. The early start and high cadence of our data permit a detailed study of the transition in SN Ia from features dominated by high-velocity components to features with exclusively photospheric components. The -14d and -13d spectra in our sample are the first to clearly resolve high-velocity Si II 6355 as a separate feature and not part of a blend with the photospheric component. HV features are found in a narrow range of velocities with a dispersion of less than 2000 km/s from -12d to -5d. PS features are clearly detected at -12d and become stronger through the time of B-max. The HV and PS regions maintain a constant separation of about 8000 km/s. With a complete picture of the contributions from both HV and PS features, we can place early observations of other SN Ia in context and show that HV features from multiple lines appear in SN Ia for nearly all observations obtained more than 10d before maximum brightness.
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http://arxiv.org/abs/1302.3537
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