Nebular-phase spectra of nearby Type Ia Supernovae

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 Ha 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.US National Science Foundation (NSF) [AST-1313484]; NASA's Astrophysics Data Analysis Program [NNX13AF35G]; Gemini Observatory [GS-2013A-Q-10, GS-2013B-Q-48, GS-2015B-Q-62, GS-2016A-Q-61]; W. M. Keck Foundation; Richard & Rhoda Goldman Fund; Christopher R. Redlich Fund; TABASGO Foundation; NSF [AST-1211916, PHY-1607611, AST-1517649]; Miller Institute for Basic Research in Science (U.C. Berkeley); NASA through the Einstein Fellowship Program [PF6-170148]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu