Wynn, GA, Braker, I, Page, KL, Casewell, SL, Longstaff, ES, Williams, PKG and Maxted, PFL (2019) Signs of accretion in the white dwarf + brown dwarf binary NLTT5306. Monthly Notices of the Royal Astronomical Society, 484 (2). 2566 - 2574.

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Abstract

We present new XSHOOTER spectra of NLTT5306, a 0.44 ± 0.04 M⊙ white dwarf in a short period (101 min) binary system with a brown dwarf companion that is likely to have previously undergone common envelope evolution. We have confirmed the presence of H α emission and discovered Na i absorption associated with the white dwarf. These observations are indicative of accretion. Accretion is typically evidenced by high-energy emission in the UV and X-ray regime. However our Swift observations covering the full orbital period in three wavebands (uvw1, uvm2, uvw2) revealed no UV excess or modulation. We used the X-ray non-detection to put an upper limit on the accretion rate of 2 × 10−15 M⊙ yr−1. We compare NLTT5306 to similar accreting binaries with brown dwarf donors and suggest the inferred accretion rate could be from wind accretion or accretion from a debris/dust disc. The lack of evidence for a disc implies NLTT5306 is magnetically funnelling a weak wind from a potentially low-gravity brown dwarf. The upper limit on the accretion rate suggests a magnetic field as low as 0.45 kG would be sufficient to achieve this. If confirmed this would constitute the first detection of a brown dwarf wind and could provide useful constraints on mass-loss rates.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2019 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: binaries: close, stars: brown dwarfs, white dwarfs
Subjects: Q Science > QB Astronomy > QB460 Astrophysics
Divisions: Faculty of Natural Sciences > School of Chemical and Physical Sciences
Depositing User: Symplectic
Date Deposited: 11 Apr 2019 09:12
Last Modified: 11 Apr 2019 09:26
URI: http://eprints.keele.ac.uk/id/eprint/6179

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