@article{f69e28ffd4bc419b9e65b24d51f66bc0,
title = "Nebular-phase spectra of nearby Type Ia Supernovae",
abstract = "We present late-time spectra of eight Type Ia supernovae (SNe Ia) obtained at > 200 d after peak brightness using the Gemini South and Keck telescopes. All of the SNe Ia in our sample were nearby, well separated from their host galaxy's light, and have early-time photometry and spectroscopy from the Las Cumbres Observatory. Parameters are derived from the light curves and spectra such as peak brightness, decline rate, photospheric velocity and the widths and velocities of the forbidden nebular emission lines. We discuss the physical interpretations of these parameters for the individual SNe Ia and the sample in general, including comparisons to well-observed SNe Ia from the literature. There are possible correlations between early-time and late-time spectral features that may indicate an asymmetric explosion, so we discuss our sample of SNe within the context ofmodels for an offset ignition and/or white dwarf collisions. A subset of our late-time spectra are uncontaminated by host emission, and we statistically evaluate our non-detections of Hα emission to limit the amount of hydrogen in these systems. Finally, we consider the late-time evolution of the iron emission lines, finding that not all of our SNe follow the established trend of a redward migration at > 200 d after maximum brightness.",
keywords = "ASASSN-14jg, SN2012hr, SN2013aa, SN2013cs, SN2013dy, SN2013gy, SN2015F, Supernovae: general, Supernovae: individual: SN2012fr",
author = "Graham, {M. L.} and S. Kumar and G. Hosseinzadeh and D. Hiramatsu and I. Arcavi and Howell, {D. A.} and S. Valenti and Sand, {D. J.} and Parrent, {J. T.} and C. McCully and Filippenko, {A. V.}",
note = "Funding Information: We thank our anonymous referee for a thoughtful and constructive review. We also thank Or Graur and R{\'e}gis Cartier for their useful feedback on this work. This research makes use of observations from the LCO and is supported by US National Science Foundation (NSF) grant AST-1313484.We made use of Swift/UVOT data reduced by P. J. Brown and released in the SOUSA. SOUSA is supported by NASA's Astrophysics Data Analysis Program through grant NNX13AF35G. This work is based in part on observations and discoveries from the KAIT at Lick Observatory. We are grateful to the staff at Lick Observatory for their assistance. 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. Research at Lick Observatory is partially supported by a generous gift from Google. We also used observations obtained at the Gemini Observatory, acquired through the Gemini Observatory Archive through programmes GS-2013A-Q-10, GS-2013B-Q-48, GS-2015B-Q-62, and GS-2016A-Q-61 and processed using the Gemini IRAF package, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnolog{\'i}a e Innovaci{\'o}n Productiva (Argentina), and Minist{\'e}rio da Ci{\^e}ncia, Tecnologia e Inova{\c c}{\~a}o (Brazil). We thank the queue service observers and technical support staff at Gemini Observatory for their assistance with the acquisition and reduction of our data. This work is based in part on observations from the LRIS at the Keck-1 telescope. We are grateful to the staff at the Keck Observatory for their assistance, and we extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. The W. M. Keck Observatory is operated as a scientific partnership amongst the California Institute of Technology, the University of California and NASA; it was made possible by the generous financial support of the W. M. Keck Foundation. We thank Daniel Perley7 and S. Bradley Cenko for the use of, and assistance with, their Keck LRIS imaging and spectroscopy reduction pipelines. We also thank Patrick Kelly, WeiKang Zheng, Isaac Shivvers and Brad Tucker for their assistance with some of the observations. The supernova research of AVF's group at U.C. Berkeley is supported by Gary & Cynthia Bengier, the Richard & Rhoda Goldman Fund, the Christopher R. Redlich Fund, the TABASGO Foundation, NSF grant AST-1211916, and the Miller Institute for Basic Research in Science (U.C. Berkeley). AVF's work was conducted in part at the Aspen Center for Physics, which is supported by NSF grant PHY-1607611; he thanks the Center for its hospitality during the neutron stars workshop in 2017 June and July. This research has made use of the online repository of data from the long-term Berkeley Supernova Project that is publicly available at http://heracles.astro.berkeley.edu/sndb/. Support for IA was provided by NASA through the Einstein Fellowship Program, grant PF6-170148. DJS acknowledges support from NSF grant AST-1517649. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Thiswork hasmade use of theWeizmann interactive supernova data repository presented by Yaron & Gal-Yam (2012) and accessible at http://wiserep.weizmann.ac.il. This work has made use of the Open Supernova Catalog that is publicly available at https://sne.space/, presented by Guillochon et al. (2017). We thank the OSC creators for their quick responses to our questions. This work has made use of the free, online, collaborative article-writing website www.authorea.com.We thank the staff at Authorea for their responsive assistance during the preparation of this document. Publisher Copyright: {\textcopyright} 2018 The Author(s).",
year = "2017",
doi = "10.1093/MNRAS/STX2224",
language = "English (US)",
volume = "472",
pages = "3437--3454",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "3",
}