Simon, Joshua D. and Gal-Yam, Avishay and Gnat, Orly and Quimby, Robert M. and Ganeshalingam, Mohan and Silverman, Jeffrey M. and Blondin, Stephane and Li, Weidong and Filippenko, Alexei V. and Wheeler, J. Craig and Kirshner, Robert P. and Patat, Ferdinando and Nugent, Peter and Foley, Ryan J. and Vogt, Steven S. and Butler, R. Paul and Peek, Kathryn M. G. and Rosolowsky, Erik and Herczeg, Gregory J. and Sauer, Daniel N. and Mazzali, Paolo A. (2009) Variable Sodium Absorption in a Low-extinction Type Ia Supernova. Astrophysical Journal, 702 (2). pp. 1157-1170. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20090914-141715190
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Recent observations have revealed that some Type Ia supernovae exhibit narrow, time-variable Na I D absorption features. The origin of the absorbing material is controversial, but it may suggest the presence of circumstellar gas in the progenitor system prior to the explosion, with significant implications for the nature of the supernova (SN) progenitors. We present the third detection of such variable absorption, based on six epochs of high-resolution spectroscopy of the Type Ia supernova SN 2007le from the Keck I Telescope and the Hobby-Eberly Telescope. The data span a time frame of approximately three months, from 5 days before maximum light to 90 days after maximum. We find that one component of the NaID absorption lines strengthened significantly with time, indicating a total column density increase of ~2.5 × 10^(12) cm^(–2). The data limit the typical timescale for the variability to be more than 2 days but less than 10 days. The changes appear to be most prominent after maximum light rather than at earlier times when the ultraviolet flux from the SN peaks. As with SN 2006X, we detect no change in the Ca II H and K absorption lines over the same time period, rendering line-of-sight effects improbable and suggesting a circumstellar origin for the absorbing material. Unlike the previous two supernovae exhibiting variable absorption, SN 2007le is not highly reddened (E_(B – V) = 0.27 mag), also pointing toward circumstellar rather than interstellar absorption. Photoionization calculations show that the data are consistent with a dense (10^7 cm^(–3)) cloud or clouds of gas located ~0.1 pc (3 × 10^(17) cm) from the explosion. These results broadly support the single-degenerate scenario previously proposed to explain the variable absorption, with mass loss from a nondegenerate companion star responsible for providing the circumstellar gas. We also present possible evidence for narrow Hα emission associated with the SN, which will require deep imaging and spectroscopy at late times to confirm.
|Additional Information:||© 2009 American Astronomical Society. Print publication: Issue 2 (2009 September 10); received 2009 May 1; accepted for publication 2009 July 15; published 2009 August 19. The authors wish to acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community.We are most fortunate to have the opportunity to conduct observations from this mountain. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly. We thank Xavier Prochaska for his work on developing the HIRES data reduction pipeline and answering all of our extensive questions about it. We also thank the anonymous referee for constructive suggestions and acknowledge helpful conversations with Chris Burns, Mark Phillips, Doug Leonard, and Juna Kollmeier. Some calculations described in this paper were performed with version 07.02 of Cloudy, last described by Ferland et al. (1998). This research has made use of NASA’s Astrophysics Data System Bibliographic Services and the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. J.D.S. acknowledges the support of a Millikan Fellowship provided by Caltech and a Vera Rubin Fellowship from the Carnegie Institution of Washington. A.G. acknowledges support by the Israeli Science Foundation; an EU Seventh Framework Programme Marie Curie IRG fellowship; the Ministry of Science, Culture & Sport, Israel and the Ministry of Research, France; and the Benoziyo Center for Astrophysics, UKWeizmann fund, a research grant from the Peter and Patricia Gruber Awards, and the William Z. and Eda Bess Novick New Scientists Fund at the Weizmann Institute. R.Q. and J.C.W. are supported in part by NSF grant AST–0707769. A.V.F.’s supernova group at U.C. Berkeley is supported by NSF grant AST–0607485, US Department of Energy grant DE-FG02- 08ER41563, and the TABASGO Foundation. KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the NSF, the University of California, the Sylvia & Jim Katzman Foundation, and the TABASGO Foundation. Supernova research at the Harvard College Observatory is supported in part by the NSF through AST– 0606772. Facilities: Keck:I (HIRES)|
|Subject Keywords:||circumstellar matter; supernovae: general; supernovae: individual (SN 1999cl, SN 2006X, SN 2007le)|
|Official Citation:||Variable Sodium Absorption in a Low-extinction Type Ia Supernova Joshua D. Simon, Avishay Gal-Yam, Orly Gnat, Robert M. Quimby, Mohan Ganeshalingam, Jeffrey M. Silverman, Stephane Blondin, Weidong Li, Alexei V. Filippenko, J. Craig Wheeler, Robert P. Kirshner, Ferdinando Patat, Peter Nugent, Ryan J. Foley, Steven S. Vogt, R. Paul Butler, Kathryn M. G. Peek, Erik Rosolowsky, Gregory J. Herczeg, Daniel N. Sauer, and Paolo A. Mazzali 2009 ApJ 702 1157-1170 doi: 10.1088/0004-637X/702/2/1157|
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|Deposited By:||Jason Perez|
|Deposited On:||15 Sep 2009 17:26|
|Last Modified:||26 Dec 2012 11:22|
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