Discovery of a Possible Cool White Dwarf Companion from the AllWISE Motion Survey
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2016
- DOI:
- 10.3847/0004-637X/832/1/62
- arXiv:
- arXiv:1609.07435
- Bibcode:
- 2016ApJ...832...62F
- Keywords:
-
- brown dwarfs;
- solar neighborhood;
- stars: individual: WISEA 0615–1247;
- stars: low-mass;
- subdwarfs;
- white dwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- doi:10.3847/0004-637X/832/1/62