Astronomers using the Hubble Space Telescope (HST) have captured critical new data on a rare eclipsing binary system, WD1032+011, composed of a white dwarf and a brown dwarf. The findings, published on September 10 on the arXiv preprint server, offer fresh insights into the nature of these systems, which are considered particularly rare in the cosmos.
A Rare Stellar Pair
White dwarf (WD)–brown dwarf (BD) binaries are scarce due to the difficulty brown dwarfs face in surviving the later stages of their companion star’s evolution. As stars evolve into white dwarfs, they can engulf nearby objects like brown dwarfs. Despite large-scale sky surveys detecting thousands of white dwarfs, only about 0.1% to 0.5% are thought to have brown dwarf companions.
WD1032+011 is an especially intriguing system because it is both eclipsing and tidally-locked. The two stars orbit each other in just 0.09 days (about 2 hours), with an inclination of 87.5 degrees and a separation of only 0.003 astronomical units (AU), making their interaction highly dynamic and easy to observe during eclipses.
Hubble's Detailed Observations
A team of astronomers led by Jenni R. French from the University of Leicester, UK, employed Hubble’s Wide Field Camera 3 (WFC3) to obtain time-resolved spectrophotometric data of WD1032+011. The Hubble data produced a broadband light curve, revealing the brown dwarf's full occultation of the white dwarf during its primary eclipse.
These observations provided detailed information about the brown dwarf’s temperature. The dayside temperature of WD1032+011B was measured at 1,748 K, while its nightside temperature was 1,555 K. The brown dwarf's spectral type is most likely L1 peculiar, and evidence suggests it has a cloud-free atmosphere.
An Inflated Brown Dwarf
One of the most remarkable findings is the inflated nature of the brown dwarf in the system. WD1032+011B has a radius of about 0.1 solar radii—larger than expected for an object of its type. This inflation is likely due to the constant irradiation from its white dwarf companion. Notably, WD1032+011B is the only known inflated brown dwarf in an eclipsing WD–BD binary.
The white dwarf, WD1032+011A, has a radius of 0.015 solar radii and an effective temperature of approximately 9,950 K. The system itself is located some 1,020 light years from Earth and is estimated to be over five billion years old.
A Potential Cataclysmic Variable?
The observations suggest that WD1032+011 could be a cataclysmic variable—a type of binary system where material from the brown dwarf may eventually transfer to the white dwarf. While no direct evidence of magnetism has been detected in WD1032+011A’s spectrum, which would confirm this hypothesis, the properties of the system are consistent with known cataclysmic variables.
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