Relative likelihood of the presence of a companion planet to WD 1856 b as a function of its mass and orbital period, assuming a circular and coplanar orbit (inclination of 90° and eccentricity of 0), with only data from HAO in the upper graph. This figure is analogous to Fig. 4, which covers a narrower range of masses using the full set of observations but uses the same colour scale and orbital period axis. This lower figure is analogous to Fig. 4, and uses the same colour scale and range of orbital periods, while covering a much wider range of masses. We find that data from small observatories such as HAO could identify companions in the brown dwarf mass range, but probing Jupiter-mass planets requires more precise transit times from larger (8–10 m-class) telescopes.