Discovery of a Possible Cool White Dwarf Companion from the AllWISE Motion Survey

Creators: Fajardo-Acosta, Sergio B.; Kirkpatrick, J. Davy; Schneider, Adam C.; Cushing, Michael C.; Stern, Daniel; Gelino, Christopher R.; Bardalez-Gagliuffi, Daniella C.; Kellogg, Kendra; Wright, Edward L.

Abstract

We present optical and near-infrared spectroscopy of WISEA J061543.91−124726.8, which we rediscovered as a high motion object in the AllWISE survey. The spectra of this object are unusual; while the red optical (λ > 7000 Å) and near-infrared spectra exhibit characteristic TiO, VO, and H_2O bands of a late-M dwarf, the blue portion of its optical spectrum shows a significant excess of emission relative to late-M-type templates. The excess emission is relatively featureless, with the exception of a prominent and very broad Na I D doublet. We find that no single, ordinary star can reproduce these spectral characteristics. The most likely explanation is an unresolved binary system of an M7 dwarf and a cool white dwarf. The flux of a cool white dwarf drops in the optical red and near-infrared, due to collision-induced absorption, thus allowing the flux of a late-M dwarf to show through. This scenario, however, does not explain the Na D feature, which is unlike that of any known white dwarf, but which could perhaps be explained via unusual abundance or pressure conditions.

Additional Information

© 2016 The American Astronomical Society. Received 2016 April 22; revised 2016 September 16; accepted 2016 September 17; published 2016 November 17. We thank our referee, Derek Homeier, for suggestions and corrections that greatly improved the manuscript. We also thank Hugh Harris and Samir Salim for very useful discussions that greatly benefited this paper, and Samir Salim for allowing us to use unpublished data. This publication makes use of data products from WISE, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory (JPL)/California Institute of Technology (Caltech), funded by the National Aeronautics and Space Administration (NASA). This research has made use of the NASA/Infrared Processing and Analysis Center (IPAC) Infrared Science Archive, which is operated by JPL/Caltech, under contract with NASA. This publication also makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and IPAC/Caltech, funded by NASA and the National Science Foundation (NSF). The DENIS project has been partly funded by the SCIENCE and the HCM plans of the European Commission under grants CT920791 and CT940627. It is supported by INSU, MEN, and CNRS in France, by the State of Baden-Württemberg in Germany, by DGICYT in Spain, by CNR in Italy, by FFwFBWF in Austria, by FAPESP in Brazil, by OTKA grants F-4239 and F-013990 in Hungary, and by the ESO C&EE grant A-04-046. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, NSF, the U.S. Department of Energy, NASA, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web Site is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions.

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