Emission lines in the atmosphere of the irradiated brown dwarf WD0137-349B
Abstract
We present new optical and near-infrared spectra of WD0137-349; a close white dwarf-brown dwarf non-interacting binary system with a period of ≈114 min. We have confirmed the presence of H α emission and discovered He, Na, Mg, Si, K, Ca, Ti and Fe emission lines originating from the brown-dwarf atmosphere. This is the first brown-dwarf atmosphere to have been observed to exhibit metal emission lines as a direct result of intense irradiation. The equivalent widths of many of these lines show a significant difference between the day-side and night-side of the brown dwarf. This is likely an indication that efficient heat redistribution may not be happening on this object, in agreement with models of hot Jupiter atmospheres. The H α line strength variation shows a strong phase dependency as does the width. We have simulated the Ca II emission lines using a model that includes the brown-dwarf Roche geometry and limb darkening, and we estimate the mass ratio of the system to be 0.135 ± 0.004. We also apply a gas-phase equilibrium code using a prescribed drift-phoenix model to examine how the chemical composition of the brown-dwarf upper atmosphere would change given an outward temperature increase, and discuss the possibility that this would induce a chromosphere above the brown-dwarf atmosphere.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2017
- DOI:
- 10.1093/mnras/stx1786
- arXiv:
- arXiv:1707.05793
- Bibcode:
- 2017MNRAS.471.1728L
- Keywords:
-
- binaries: close;
- brown dwarfs;
- white dwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 10 pages, 7 figures, 2 tables