Gemini/GMOS Transmission Spectroscopy of the Grazing Planet Candidate WD 1856+534 b

Abstract

WD 1856+534 b is a Jupiter-sized, cool giant planet candidate transiting the white dwarf WD 1856+534. Here, we report an optical transmission spectrum of WD 1856+534 b obtained from ten transits using the Gemini Multi-Object Spectrograph. This system is challenging to observe due to the faintness of the host star and the short transit duration. Nevertheless, our phase-folded white light curve reached a precision of 0.12%. WD 1856+534 b provides a unique transit configuration compared to other known exoplanets: the planet is 8× larger than its star and occults over half of the stellar disk during mid-transit. Consequently, many standard modeling assumptions do not hold. We introduce the concept of a “limb darkening corrected, time-averaged transmission spectrum” and propose that this is more suitable than ( R p , λ / 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 WD 1856+534 b to be >0.84 M J (to 2σ confidence), assuming a clear atmosphere and a Jovian composition. High-altitude cloud decks can allow lower masses. WD 1856+534 b could have formed either as a result of common envelope evolution or migration under the Kozai–Lidov mechanism. Further studies of WD 1856+534 b, alongside new dedicated searches for substellar objects around white dwarfs, will shed further light on the mysteries of post-main-sequence planetary systems.

Giant Planet Engulfment by Evolved Giant Stars: Light Curves, Asteroseismology, and Survivability

“…The transiting planet WD 1856+534 b (Vanderburg et al 2020) orbits a (0.58 ± 0.04) M e WD at a separation of 0.02 au (≈4 R e ). Its mass is constrained to be 0.84 M J < M p < 13.8 M J (Vanderburg et al 2020;Xu et al 2021). Our MESA simulations suggest that a planet would struggle to avoid tidal disruption through most of the allowed mass range, even if it succeeded in ejecting the envelope with the aid of dust-driven winds.…”

Common envelope evolution and triple dynamics as potential pathways to form the inner white dwarf + brown dwarf binary of the triple star system Gaia 0007−1605

“…While common envelope evolution is disfa v oured for masses below 5 M jup , ZLK oscillations also co v er lower masses being the most likely scenario below 3 M jup . Unfortunately, according to the lower limits derived from transmission spectroscopy that appear in the literature (0.84 and 2.4 M jup at there 2 σ level, Alonso et al 2021 ;Xu et al 2021 ) both scenarios remain plausible.…”