Kavli Affiliate: Avi Shporer
| First 5 Authors: Patrick Tamburo, Samuel W. Yee, Juliana García-Mejía, David Charbonneau, Allyson Bieryla
| Summary:
TOI-3884~b is an unusual 6.4~R$_oplus$ planet orbiting an M4 host, whose
transits display large and persistent spot-crossing events. We used the
textit{Tierras} Observatory to monitor both the long-term photometric
variability of TOI-3884 and changes in the spot-crossing events across multiple
transits of the planet. We show that the star rotates with a period of $11.021
pm 0.014$~days. We simultaneously model the rotational modulation of the star
and variations in transit shapes that arise due to rotation of the spot,
allowing us to determine the true stellar obliquity, $psi_star$. The data are
best described by a planet on a misaligned orbit around a highly inclined star
($psi_star = {76.1^circ} ^{+2.2^circ}_{-2.6^circ}$; $i_star =
{24.4^circ}^{+1.8^circ}_{-1.4^circ}$) that hosts a large polar starspot
($r_mathrm{spot} = {33.1^circ}^{+2.0^circ}_{-1.9^circ}$;
$lambda_mathrm{spot} = {79.4^circ}^{+1.4^circ}_{-1.2^circ}$). Archival
photometry from the Zwicky Transient Facility suggests that this polar spot has
persisted on TOI-3884 for at least seven years. The TOI-3884 system provides a
benchmark for studying the evolution of a polar spot on an M dwarf.
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