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arXiv · 1609.07435

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

Sergio B. Fajardo-Acosta·J. Davy Kirkpatrick·Adam C. Schneider·Michael C. Cushing·Daniel Stern·Christopher R. Gelino·Daniella C. Bardalez-Gagliuffi·Kendra Kellogg·Edward L. Wright
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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>$ 7,000 Å) and near-infrared spectra exhibit characteristic TiO, VO, and H$_{2}$O 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.

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Sergio B. Fajardo-Acosta, J. Davy Kirkpatrick, Adam C. Schneider, Michael C. Cushing, Daniel Stern, Christopher R. Gelino, Daniella C. Bardalez-Gagliuffi, Kendra Kellogg, Edward L. Wright. 2016-09-23. Discovery of a Possible Cool White Dwarf Companion from the AllWISE Motion Survey. https://doi.org/10.3847/0004-637x%2F832%2F1%2F62

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