Brown Dwarf Binaries and the Brown Dwarf Desert

Brown Dwarf Binaries and the Brown Dwarf Desert

Physics

Callum J. Hodge

2025

The Brown Dwarf Desert, encapsulating the bias of brown dwarf companions towards wide separations (>1000AU), means that transiting brown dwarfs should be rare phenomena. The following study investigates this claim by simulating a model population of all transiting brown dwarfs in the Solar neighbourhood using existing expected distributions of brown dwarf properties. Initial results found a significant underdensity of these objects compared to the current numbers detected by TESS as a result of typically wider separations in the model population. Modifying this population with a power-law separation distribution found that an exponent of α>0.405 is necessary for making the model population agree with the TESS data. Likewise, a log-normal distribution requires a mean of μ<0.4 (equivalent to a peak in the distribution <2.5AU) and a standard deviation of 0.6<σ<1.0, yet this must also be combined with an increase in the binary fraction of f>3.7%. This highlights the alarming contradiction between our current understanding of the Brown Dwarf Desert and the number of transiting brown dwarfs that have been discovered, meaning a refinement of separation models is necessary.

brown dwarf, binary systems, Solar neighbourhood, transit, separation, Brown Dwarf Desert