Gemini/GMOS transmission spectroscopy of WD 1856+534 b

We introduce the concept of a "limb darkening corrected, time-averaged transmission spectrum" and propose that this is more suitable than (R_p,{lambda}_/R_s_)^2^ for comparisons to atmospheric models for planets with grazing transits. We also present a modified radiative transfer prescription. Though the transmission spectrum shows no prominent absorption features, it is sufficiently precise to constrain the mass of WD1856+534b to be >0.84M_J_ (to 2{sigma} confidence), assuming a clear atmosphere and a Jovian composition.

High-altitude cloud decks can allow lower masses. WD1856+534b could have formed either as a result of common envelope evolution or migration under the Kozai-Lidov mechanism. Further studies of WD1856+534b, alongside new dedicated searches for substellar objects around white dwarfs, will shed further light on the mysteries of post-main-sequence planetary systems.