* Astronomy

Title: High-Velocity Line-Forming Regions in the Type Ia Supernova 2009ig
Authors: G. H. "Howie" Marion (1), Jozsef Vinko (2 and 3), J. Craig Wheeler (2), Ryan J. Foley (1 and 4), Eric Y. Hsiao (5), Peter J. Brown (6), Peter Challis (1), Alexei V. Filippenko (7), Peter Garnavich (8), Robert P. Kirshner (1), Wayne B. Landsman (9), Jerod T. Parrent (10 and 11), Tyler A. Pritchard (12), Peter W. A. Roming (12 and 13), Jeffrey M. Silverman (2), Xiaofeng Wang (14 and 6) ((1) Harvard-Smithsonian Centre for Astrophysics, (2) University of Texas at Austin, (3) Department of Optics and Quantum Electronics, University of Szeged, (4) Clay Fellow, Harvard-Smithsonian Centre for Astrophysics, (5) Carnegie Observatories, Las Campanas Observatory, (6) Mitchell Institute, Texas A&M University, (7) Department of Astronomy, University of California, (8) Department of Physics, University of Notre Dame, (9) Adnet Systems, NASA Goddard Space Flight Center, (10) Las Cumbres Observatory Global Telescope Network, (11) Department of Physics & Astronomy, Dartmouth College, (12) Department of Astronomy & Astrophysics, Penn State University, (13) Space Science & Engineering Division, Southwest Research Institute, (14) Physics Department and Tsinghua Centre for Astrophysics (THCA))

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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