Open AccessThe nature of the close magnetic white dwarf + probable brown dwarf binary SDSS J121209.31+013627.7 ★
Author(s) -
Burleigh M. R.,
Marsh T. R.,
Gänsicke B. T.,
Goad M. R.,
Dhillon V. S.,
Littlefair S. P.,
Wells M.,
Bannister N. P.,
Hurkett C. P.,
Martindale A.,
Dobbie P. D.,
Casewell S. L.,
Baker D. E. A.,
Duke J.,
Farihi J.,
Irwin M. J.,
Hewett P. C.,
Roche P.,
Lewis F.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.11030.x
Subject(s) - physics , white dwarf , astrophysics , intermediate polar , cataclysmic variable star , rotation period , roche lobe , orbital period , accretion (finance) , astronomy , photometry (optics) , dwarf nova , polar , circumbinary planet , brown dwarf , light curve , ephemeris , stars , satellite
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.