The Subluminous and Peculiar Type Ia Supernova PTF 09dav

Creators: Sullivan, M.; Kasliwal, M. M.; Nugent, P. E.; Howell, D. A.; Thomas, R. C.; Ofek, E. O.; Arcavi, I.; Blake, S.; Cooke, J.; Gal-Yam, A.; Hook, I. M.; Mazzali, P.; Podsiadlowski, P.; Quimby, R.; Bildsten, L.; Bloom, J. S.; Cenko, S. B.; Kulkarni, S. R.; Law, N.; Poznanski, D.

Abstract

PTF 09dav is a peculiar subluminous Type Ia supernova (SN) discovered by the Palomar Transient Factory (PTF). Spectroscopically, it appears superficially similar to the class of subluminous SN1991bg-like SNe, but it has several unusual features which make it stand out from this population. Its peak luminosity is fainter than any previously discovered SN1991bg-like SN Ia (MB ~ –15.5), but without the unusually red optical colors expected if the faint luminosity were due to extinction. The photospheric optical spectra have very unusual strong lines of Sc II and Mg I, with possible Sr II, together with stronger than average Ti II and low velocities of ~6000 km s^(–1). The host galaxy of PTF09dav is ambiguous. The SN lies either on the extreme outskirts (~41 kpc) of a spiral galaxy or in an very faint (MR ≥ –12.8) dwarf galaxy, unlike other 1991bg-like SNe which are invariably associated with massive, old stellar populations. PTF 09dav is also an outlier on the light-curve-width-luminosity and color-luminosity relations derived for other subluminous SNe Ia. The inferred ^(56)Ni mass is small (0.019 ± 0.003 M_☉), as is the estimated ejecta mass of 0.36 M_☉. Taken together, these properties make PTF 09dav a remarkable event. We discuss various physical models that could explain PTF 09dav. Helium shell detonation or deflagration on the surface of a CO white dwarf can explain some of the features of PTF 09dav, including the presence of Sc and the low photospheric velocities, but the observed Si and Mg are not predicted to be very abundant in these models. We conclude that no single model is currently capable of explaining all of the observed signatures of PTF 09dav.

Additional Information

© 2011 American Astronomical Society. Received 2010 December 12; accepted 2011 March 9; published 2011 April 26. We acknowledge useful discussions with Brian Schmidt and Dan Kasen. We thank Richard Ellis for providing the P200/ DBSP spectrum. M.S. acknowledges support from the Royal Society. E.O.O. is supported by an Einstein fellowship and NASA grants. L.B. is supported by the National Science Foundation under grants PHY 05-51164 and AST 07-07633. S.B.C. acknowledges generous support from Gary and Cynthia Bengier and the Richard and Rhoda Goldman Foundation. D.P. is supported by an Einstein fellowship. The WHT is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Observations obtained with the Samuel Oschin Telescope and the 60 inch Telescope at the Palomar Observatory as part of the Palomar Transient Factory project, a scientific collaboration between the California Institute of Technology, Columbia University, Las Cumbres Observatory, the Lawrence Berkeley National Laboratory, the National Energy Research Scientific Computing Center, the University of Oxford, and the Weizmann Institute of Science. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. 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 the National Aeronautics and Space Administration. The Weizmann Institute participation of in PTF is supported in part by grants from the Israeli Science Foundation to A.G. Weizmann-Caltech collaborative work on PTF is supported by a grant from the Binational Science Foundation (BSF) to A.G. and S.R.K. Collaborative work by A.G. and M.S. is supported by a grant from the Weizmann-UK "making connection" program. Collaborative work of A.G. and P.A.M. is supported by a Weizmann-Minerva grant. A.G. is supported by an EU/FP7 Marie Curie IRG fellowship and a research grant from the Peter and Patricia Gruber Awards. Facilities: PO:1.2m, ING: Herschel, PO:1.5m, Hale, Keck:I, LCOGT

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