The Oblique Orbit of WASP-107b from K2 Photometry
Author(s)
Winn, Joshua N.; Dai, Fei
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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.
Date issued
2017-04Department
Massachusetts Institute of Technology. Department of Physics; MIT Kavli Institute for Astrophysics and Space ResearchJournal
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
ISSN
1538-3881
0004-6256