A brown dwarf donor in an accreting binary
Authors: Stuart Littlefair, Vik Dhillon (both University of Sheffield, UK), Tom Marsh, Boris Gaensicke, John Southworth (all Warwick University) and Chris Watson (University of Sheffield).
This webpage by Stuart Littlefair.
Call +44 (0)114 2224525
The paper appears in Science, 8th December 2006
Embargoed: Not for Release Until 2:00 pm U.S. ET Thursday, 07 December 2006
Astronomers found a binary star class that had been predicted, but not yet seen. Called cataclysmic variables, these flickering binary star systems contain a compact white dwarf that sucks material from its larger companion star, eventually causing the white dwarf to cease hydrogen burning and becomes a brown dwarf. Theory held that most short period systems should have already evolved to brown dwarfs. Stuart Paul Littlefair and colleagues accurately timed the eclipses in a short period cataclysmic variable system and showed that the donor is a brown dwarf 5 percent of the Sun's mass. Because the star's mass is higher than its orbital period would suggest, the brown dwarf radii may be underestimated by current evolutionary models. Pierre F. L. Maxted discusses this in a related Perspective. This research appears in the 08 December 2006 issue of the journal Science.
Caption: Artist's impression of SDSS 1035+0551. The
hot white dwarf is the same size as the Earth, yet weighs the same as
our Sun. The brown dwarf is about the same size as Jupiter, but much
more massive. The gravity of the white dwarf pulls gas from the brown
dwarf; this gas spirals down onto the surface of the white dwarf, like
water down a plughole, forming an "accretion disc" of hot gas around
the white dwarf. Where the falling gas from the brown dwarf hits the
accretion disc, it creates a hot spot. The position of this hot spot
depends on the masses of the two stars. The authors precisely timed
when the white dwarf and hot spot were eclipsed by the brown
dwarf. This allowed them to measure the location of the hot spot, and
infer the masses of the two stars.
Full size JPG (2100x1500 pixels)
Facts and Figures
SDSS 103533.03+055158.4
Near the edge of the constellation Sextans
Distance: 750 light years (230 pc)
Separation of two stars: 0.62 solar radii
Orbital Period: 82.1 minutes
g' magnitude ~ 18
White Dwarf
Mass: same mass as Sun (0.94 Solar masses)
Radius: same size as Earth (0.95 Earth radii)
Temperature: 10100K
Density: one teaspoon weighs ten tonnes
Brown Dwarf
Mass: 54 Jupiter Masses (0.052 Solar masses)
Radius: 1 Jupiter radius (0.108 Solar radii)
Density: about 50 times as dense as water, twice as dense as gold