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The nature of the close magnetic white dwarf + probable brown dwarf binary SDSS J121209.31+013627.7

journal contribution
posted on 2023-05-17, 14:34 authored by Burleigh, MR, Marsh, TR, Gansicke, BT, Goad, MR, Dhillon, VS, Littlefair, SP, Wells, M, Bannister, NP, Hurkett, CP, Martindale, A, Dobbie, PD, Casewell, SL, Baker, DEA, Duke, J, Farihi, J, Irwin, MJ, Hewett, PC, Roche, P, Lewis, F
Optical time series photometry of the short-period magnetic white dwarf + probable brown dwarf binary SDSS J121209.31+013627.7 reveals pulse-like variability in all bands from i′ to u′, increasing towards bluer wavelengths and peaking at u′. These modulations are most likely due to a self-eclipsing accretion hot spot on the white dwarf, rotating into view every 88.43 min. This period is commensurate with the Hα radial velocity period of ≈90 min, and consistent with the rotation period of the accretor being equal to the binary orbital period. We combine our observations with other recently reported results to provide an accurate ephemeris. We also detect the system in X-rays with Swift, and estimate the accretion rate at ≈10−13 M⊙ yr−1. We suggest that SDSS J121209.31+013627.7 is most likely a magnetic cataclysmic variable in an extended state of very low accretion, similar to the well-studied polar EF Eri. Alternatively, the putative brown dwarf is not filling its Roche lobe and the system is a detached binary in which the white dwarf is efficiently accreting from the wind of the secondary. However, it is unclear whether an L dwarf wind is strong enough to provide the measured accretion rate. We suggest further observations to distinguish between the Roche lobe overflow and wind accretion scenarios.

History

Publication title

Monthly Notices of the Royal Astronomical Society

Volume

373

Issue

4

Pagination

1416-1422

ISSN

0035-8711

Department/School

School of Natural Sciences

Publisher

Blackwell Publishing Ltd

Place of publication

9600 Garsington Rd, Oxford, England, Oxon, Ox4 2Dg

Rights statement

Copyright 2006 The Authors. Journal compilation 2006 RAS, MNRAS 373

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