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KELT-9 b’s Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin–Orbit Misalignment
Name
Ahlers_2020_AJ_160_4.pdf
Description
Published version
Size
1.83 MB
Format
Adobe PDF
Checksum (MD5)
f1407ca33c40bffa095d1f54609d8df4
Author(s)
Ahlers, John P
Johnson, Marshall C
Stassun, Keivan G
Colón, Knicole D
Barnes, Jason W
Stevens, Daniel J
Beatty, Thomas
Gaudi, B Scott
Collins, Karen A
Rodriguez, Joseph E
Date Issued
2020
Journal
Astronomical Journal
Publisher
American Astronomical Society
Version
Final published version
Abstract
© 2020. The American Astronomical Society. All rights reserved KELT-9 b is an ultra-hot Jupiter transiting a rapidly rotating, oblate early-A-type star in a polar orbit. We model the effect of rapid stellar rotation on KELT-9 b's transit light curve using photometry from the Transiting Exoplanet Survey Satellite to constrain the planet's true spin-orbit angle and to explore how KELT-9 b may be influenced by stellar gravity darkening. We constrain the host star's equatorial radius to be 1.089 ± 0.017 times as large as its polar radius and its local surface brightness to vary by ∼38% between its hot poles and cooler equator. We model the stellar oblateness and surface brightness gradient and find that it causes the transit light curve to lack the usual symmetry around the time of minimum light. We take advantage of the light-curve asymmetry to constrain KELT-9 b's true spin-orbit angle (87° +10° -11° ) agreeing with Gaudi et al. that KELT-9 b is in a nearly polar orbit. We also apply a gravity-darkening correction to the spectral energy distribution model from Gaudi et al. and find that accounting for rapid rotation gives a better fit to available spectroscopy and yields a more reliable estimate for the star's polar effective temperature.
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DOI of Published Version
10.3847/1538-3881/AB8FA3
