Origin of the brown-dwarf temperature discrepancy

Determine the origin of the systematic discrepancy between the effective temperatures of observed white dwarf–brown dwarf binary companions and those predicted by the MRBIN population-synthesis simulations, including whether it arises from observational difficulties in measuring brown-dwarf properties or from systematic differences among brown-dwarf evolutionary models.

Background

The simulations reproduce the observed white-dwarf mass and temperature distributions reasonably well, but the predicted brown-dwarf effective temperatures are systematically higher than the observed values. A Kolmogorov–Smirnov test gives a very low probability that the simulated and observed brown-dwarf temperature samples are drawn from the same parent distribution. An ad hoc downward shift of approximately 550–700 K in the simulated temperatures improves the agreement, but this does not establish the physical cause of the discrepancy.

The unresolved issue may reflect substantial observational challenges in determining brown-dwarf effective temperatures and masses, or systematic differences between the evolutionary grids used to assign temperatures to simulated brown dwarfs. Resolving this discrepancy is important for validating the substellar evolutionary prescriptions used in population-synthesis predictions of white dwarf–brown dwarf binaries.

References

The origin of this discrepancy remains uncertain, although it may partly reflect the considerable observational challenges involved in determining the physical properties of BDs, particularly their effective temperatures and masses.

— The scarcity of white dwarf-brown dwarf binaries in the solar neighbourhood: A population synthesis study  (2609.03017 - Santos-García et al., 2 Sep 2026) in Section 4.3, “Comparison of the observed and simulated WD–BD populations”