Astronomers have made groundbreaking observations of an eclipsing white dwarf-brown dwarf binary system, unveiling crucial insights into the nature and evolution of these rare celestial partnerships.
Unraveling a Cosmic Rarity
The remaining cases belong to a very rare class in which white dwarfs have a brown-dwarf companion, systems that pose the challenging question on how BDs (typically far outside the giant progenitors) can survive engulfment by the WD’s progenitor.
We expect only 0.1-0.5% of white dwarfs with known cooling ages to host a brown dwarf companion in such systems. The more exciting aspect is that it produced a WD-BD binary with the abbreviated name of WD1032+011, an eclipsing, tidally-locked system with an orbit 0.09 days long and viewed from Earth at patient inclination angle of 87.5 degrees.
Led by Jenni R. French from the University of Leicester, UK, a team of astronomers used the Wide Field Camera 3 on the Hubble Space Telescope to study this unusual duo in greater detail. The researchers’ findings have revealed this extraordinary system in a new light, showing the complicated interactions that allow these two companions to coexist.
The Secrets Behind WD1032+011
The observations yielded an array of intriguing details about the two items in this binary system.
They found that the brown dwarf, WD1032+011B, had a dayside temperature of 1748 K and a nightside temperature of 1555 K. The spectral type was found to be probably peculiar L1, consistent with the fact that at these low luminosities, there are likely cloud-free atmospheres.
Even more remarkable, WD1032+011B was found to have a radius of ∼0.1 Solar radii, i.e., being an inflated brown dwarf. This is potentially as a result of the continual irradiation from the white dwarf companion, hence WD1032+011B can be thought of as being the single case in which an inflated brown-dwarf component resides in a short-period eclipsing WD-BD binary.
The white dwarf is itself a very small one at about 0.015 solar radii, with the effective temperature of 9,950 K. The entire system has an estimated distance of around 1,020 light years and should be no younger than five billion years.
Conclusion
The WD1032+011 system can help us to understand how these odd white dwarf-brown dwarf binaries form, and what they look like. The identification of an inflated brown dwarf and the potential for cataclysmic variable activity in the system provides a new territory for future investigation into the peculiar circumstances that can transpire within such enigmatic cosmic pairings.
