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

Kavli Affiliate: Andrew Vanderburg

| First 5 Authors: Siyi Xu, Hannah Diamond-Lowe, Ryan J. MacDonald, Andrew Vanderburg, Simon Blouin

| Summary:

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
$8times$ larger than its star and occults over half of the stellar disc 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
$(R_{mathrm{p}, lambda} / R_{mathrm{s}})^2$ 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$_mathrm{J}$ (to $2 , sigma$ 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.

| Search Query: ArXiv Query: search_query=au:”Andrew Vanderburg”&id_list=&start=0&max_results=10

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