A Low Stellar Obliquity for WASP-47, a Compact Multiplanet System with a Hot Jupiter and an Ultra-short Period Planet

Creators: Sanchis-Ojeda, Roberto; Winn, Joshua N.; Dai, Fei; Howard, Andrew W.; Isaacson, Howard; Marcy, Geoffrey W.; Petigura, Erik; Sinukoff, Evan; Weiss, Lauren; Albrecht, Simon; Hirano, Teruyuki; Rogers, Leslie

Abstract

We have detected the Rossiter–Mclaughlin effect during a transit of WASP-47b, the only known hot Jupiter with close planetary companions. By combining our spectroscopic observations with Kepler photometry, we show that the projected stellar obliquity is λ = 0° ± 24°. We can firmly exclude a retrograde orbit for WASP-47b, and rule out strongly misaligned prograde orbits. Low obliquities have also been found for most of the other compact multiplanet systems that have been investigated. The Kepler-56 system, with two close-in gas giants transiting their subgiant host star with an obliquity of at least 45º, remains the only clear counterexample.

Additional Information

© 2015. The American Astronomical Society. Received 2015 August 27; accepted 2015 September 17; published 2015 October 7. We thank Eugene Chiang and Rebekah Dawson for helpful discussions. We are grateful to Juliette Becker and Andrew Vanderburg for sharing their manuscript at an early stage and for making their data publicly available. This work was performed, in part, under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. This research has made use of the Exoplanet Orbit Database and the Exoplanet Data Explorer at exoplanets.org. This work was supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. Work by J.N.W. was supported by the NASA Origins program (grant code NNX11AG85G). LMW thanks Ken and Gloria Levy for their generous support. T.H. is supported by Japan Society for Promotion of Science (JSPS) Fellowship for Research (No.25- 3183). LAR gratefully acknowledges support provided by NASA through Hubble Fellowship grant #HF-51313 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agencyʼs scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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