* Astronomy

At this week's American Astronomical Society meeting in Minneapolis, Minnesota, Vanderbilt University astronomer Yilen Gómez Maqueo Chew and five colleagues presented detailed observations of the first known eclipsing binary system containing two brown dwarfs — star like gas balls not quite massive enough to sustain nuclear fusion in their cores. Seen from Earth as a single point of light, the system resides in the Orion star-forming region, V1174 Ori and is only several million years old .

Both V1174 Ori and the newly discovered system are of particular interest because they are examples of very young, low-mass stars which provide useful data for testing the predictions of current theoretical models of pre-main-sequence stellar evolution. Both systems are members of the Orion Nebula Cluster, and therefore have likely ages of only a few million years. V1174 Ori comprises a primary star of 1 solar mass and a secondary star of 0.7 solar mass.

The components of the newly discovered system are both brown dwarfs, with masses of 0.053 (with a diameter of 0.89 Sun) and 0.034 solar masses (with a diameter of 0.70 Sun), respectively, making this system the first example of an eclipsing brown dwarf pair.
Every 9.78 days, the objects complete one highly elongated orbit, with a semi major axis of 8.52 solar radii, around a common centre of mass.

Gómez Maqueo Chew's team has monitored the "star" over the past three years with the 1.3-meter SMARTS telescope at the Cerro Tololo Inter-American Observatory in Chile. The team nailed down the major characteristics of both of the system's brown dwarfs by gathering the Doppler shifts, which yield orbital velocities, and light curves, which help establish the two bodies' sizes.

As with most binary stars, the two brown dwarfs presumably formed simultaneously within the same cloud of gas. If so, conventional star-formation theory confidently predicts that the more massive member should start off hotter and take longer to dissipate the heat from its formation. But that's not what Chew and her colleagues observed. With a temperature of about 2,850° Kelvin , the smaller and less massive brown dwarf is 150° K hotter than its partner.
"We do not understand why the less massive component is hotter," - Gómez Maqueo Chew.

She says that ongoing observations may improve the team's temperature measurements and that the primary brown dwarf may turn out to be hotter, as theory predicts. Another possibility is that the brown dwarfs have different ages. If the discrepancy cannot be resolved, considerable doubt may be cast on evolutionary models that astronomers use to infer the ages of brown dwarfs and extrasolar planets whose masses cannot be measured with orbital mechanics.


Position(2000): RA: 05 34 27.8 Dec: -05 41 37