The Oblique Orbit of WASP-107b from K2 Photometry

Journal Article · Mon May 01 04:00:00 EDT 2017 · The Astronomical Journal (Online)

DOI:https://doi.org/10.3847/1538-3881/AA65D1· OSTI ID:22863096

Dai, Fei ^[1]

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1. Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

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{sub min}/R{sub ⋆}≳8). This demonstrates a connection between stellar obliquity and planet properties, in contradiction to some theories for obliquity excitation.

• OSTI ID: 22863096
• Journal Information: The Astronomical Journal (Online), Journal Name: The Astronomical Journal (Online) Journal Issue: 5 Vol. 153; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ALIGNMENT
EXCITATION
MASS
ORBITS
PHOTOMETRY
ROTATION
SATELLITES
SPIN
STARS
STARSPOTS