[vsnet-campaign 1655] SDSS J121209.31+013627.7
Taichi Kato
tkato at kusastro.kyoto-u.ac.jp
Tue Jul 18 11:41:26 JST 2006
EF Eri-like object in "permanent" low state?
magnetic CV with a brown-dwarf binary?
probably worth monitoring for long-term activity
http://xxx.lanl.gov/abs/astro-ph/0607389
The nature of the close magnetic white dwarf + probable brown dwarf
binary SDSS J121209.31+013627.7
Authors: M. R. Burleigh (1), T. R. Marsh (2), B. T. Gansicke (2), M.
R. Goad (1), V. Dhillon (3), S. P. Littlefair (3), M. Wells (4), N.
P. Bannister (1), C. P. Hurkett (1), A. Martindale (1), P. D. Dobbie
(1), S. L. Casewell (1), D. E. A. Baker (1), J. Duke (1), J. Farihi
(5), M. J. Irwin (6), P. C. Hewett (6), P. Roche (7), F. Lewis (7)
((1) Department of Physics and Astronomy, University of Leicester (2)
Department of Physics, University of Warwick (3) Department of
Physics and Astronomy, University of Sheffield, Sheffield, UK, (4)
Oundle School, Northamptonshire, UK (5) Gemini Observatory, USA, (6)
Institute of Astronomy, University of Cambridge, UK, (7) Department
of Physics and Astronomy, University of Wales, UK) Comments:
Submitted to MNRAS
Optical time series photometry of the short period magnetic white
dwarf + probable brown dwarf binary SDSS 121209.31+013627.7 reveals
pulse-like variability in all bands from i' to u', 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 minutes.
This period is commensurate with the radial velocity period
determined by Schmidt et al. 2005 of ~90 minutes, and consistent with
the rotation period of the accretor being equal to the binary orbital
period. We combine our observations with those recently published by
Koen and Maxted 2006 to provide an accurate ephemeris. We also detect
the system in X-rays with Swift, and estimate the accretion rate at
~1x10^-13Msun per year. We suggest that SDSS1212 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. Six such post-common
envelope, "pre-Polar" systems - termed "low accretion rate Polars
(LARPs)" by Schwope et al. 2002 - have previously been identified
through optical cyclotron emission lines. Cyclotron emission from
SDSS1212 has recently been detected in the near-IR Debes et al. 2006
but, if detached, it would be the first "LARP" with a probably
sub-stellar secondary. 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 over-flow
and wind accretion scenarios.
More information about the vsnet-campaign
mailing list