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

November 2016 • 2016ApJ...832...62F

Authors • 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 H₂O 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2016ApJ...832...62F
• PDF https://iopscience.iop.org/article/10.3847/0004-637X/832/1/62/pdf
• PDF https://stacks.iop.org/0004-637X/832/62/pdf
• PREPRINT http://arxiv.org/abs/1609.07435
• DATA https://irsa.ipac.caltech.edu/bibdata/2016/F/2016ApJ...832...62F.html
• ELECTR https://doi.org/10.3847%2F0004-637X%2F832%2F1%2F62