The Oblique Orbit of WASP-107b from K2 Photometry
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Dai_2017_AJ_153_205.pdf
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Author(s)
Winn, Joshua N.
Dai, Fei
Date Issued
April 2017
Journal
The Astronomical Journal
Publisher
American Astronomical Society
Citation
Dai, Fei, and Joshua N. Winn. “The Oblique Orbit of WASP-107b from K2 Photometry.” The Astronomical Journal, vol. 153, no. 5, Apr. 2017, p. 205. © 2017 The American Astronomical Society
Version
Final published version
Abstract
Observations of nine transits of WASP-107 during the K2 mission reveal three separate occasions when the planet crossed in front of a starspot. The data confirm the stellar rotation period to be 17 days - approximately three times the planet's orbital period - and suggest that large spots persist for at least one full rotation. If the star had a low obliquity, at least two additional spot crossings should have been observed. They were not observed, giving evidence for a high obliquity. We use a simple geometric model to show that the obliquity is likely in the range 40°-140°, i.e., both spin-orbit alignment and anti-alignment can be ruled out. WASP-107 thereby joins the small collection of relatively low-mass stars with a high obliquity. Most such stars have been observed to have low obliquities; all of the exceptions, including WASP-107, involve planets with relatively wide orbits ("warm Jupiters," with a[subscript min]/R∗ ≳ 8). This demonstrates a connection between stellar obliquity and planet properties, in contradiction to some theories for obliquity excitation.
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.3847/1538-3881/AA65D1
