The Oblique Orbit of WASP-107b from K2 Photometry

• Main Authors: Winn, Joshua N. (Author), Dai, Fei (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Physics (Contributor), MIT Kavli Institute for Astrophysics and Space Research (Contributor)
• Format: Article
• Language: English
• Published: American Astronomical Society, 2017-11-20T20:16:04Z.
• Subjects: Article
• Online Access: Get fulltext

 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.