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 ${({R}_{p,\lambda }/{R}_{s})}^{2}$ 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 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.
- Publication:
-
The Astronomical Journal
- Pub Date:
- December 2021
- DOI:
- 10.3847/1538-3881/ac2d26
- arXiv:
- arXiv:2110.14106
- Bibcode:
- 2021AJ....162..296X
- Keywords:
-
- 487;
- 1799;
- 2172;
- 185;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 21 pages, 10 figures, accepted for publication in AJ