A Brown Dwarf Mass Donor in an Accreting Binary
S. P. Littlefair,1*
V. S. Dhillon,1
T. R. Marsh,2
Boris T. Gänsicke,2
John Southworth,2
C. A. Watson1
A long-standing and unverified prediction of binary star evolution
theory is the existence of a population of white dwarfs accreting
from substellar donor stars. Such systems ought to be common,
but the difficulty of finding them, combined with the challenge
of detecting the donor against the light from accretion, means
that no donor star to date has a measured mass below the hydrogen
burning limit. We applied a technique that allowed us to reliably
measure the mass of the unseen donor star in eclipsing systems.
We were able to identify a brown dwarf donor star, with a mass
of 0.052 ± 0.002 solar mass. The relatively high mass
of the donor star for its orbital period suggests that current
evolutionary models may underestimate the radii of brown dwarfs.
2 Department of Physics, University of Warwick, Coventry, CV4 7AL, UK.
* To whom correspondence should be addressed. E-mail: s.littlefair{at}shef.ac.uk
