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


Burleigh, MR and Marsh, TR and Gansicke, BT and Goad, MR and Dhillon, VS and Littlefair, SP and Wells, M and Bannister, NP and Hurkett, CP and Martindale, A and Dobbie, PD and Casewell, SL and Baker, DEA and Duke, J and Farihi, J and Irwin, MJ and Hewett, PC and Roche, P and Lewis, F, The nature of the close magnetic white dwarf + probable brown dwarf binary SDSS J121209.31+013627.7, Monthly Notices of the Royal Astronomical Society, 373, (4) pp. 1416-1422. ISSN 0035-8711 (2006) [Refereed Article]

Copyright Statement

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

DOI: doi:10.1111/j.1365-2966.2006.11030.x


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.

Item Details

Item Type:Refereed Article
Keywords:low-mass stars, brown dwarfs, novae, cataclysmic variables, white dwarfs
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Stellar astronomy and planetary systems
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Dobbie, PD (Dr Paul Dobbie)
ID Code:81087
Year Published:2006
Web of Science® Times Cited:29
Deposited By:Mathematics and Physics
Deposited On:2012-11-22
Last Modified:2013-06-25

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