Emission lines in the atmosphere of the irradiated brown dwarf WD0137−349B

E. S. Longstaff, S. L. Casewell, G. A. Wynn, P. F. L. Maxted, Ch. Helling

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22 Citations (Scopus)

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.
Original languageEnglish
Pages (from-to)1728-1736
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume471
Issue number2
Early online date15 Jul 2017
DOIs
Publication statusPublished - 21 Oct 2017

Keywords

  • Binaries: close
  • Brown dwarfs
  • White dwarfs

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