Orbital Orientations of Exoplanets: HAT-P-4b is Prograde and HAT-14b is Retrograde

Creators: Winn, Joshua N.; Howard, Andrew W.; Johnson, John Asher; Marcy, Geoffrey W.; Isaacson, Howard; Shporer, Avi; Bakos, Gáspár Á.; Hartman, Joel D.; Holman, Matthew J.; Albrecht, Simon; Crepp, Justin R.; Morton, Timothy D.

Abstract

We present observations of the Rossiter-McLaughlin effect for two exoplanetary systems, revealing the orientations of their orbits relative to the rotation axes of their parent stars. HAT-P-4b is prograde, with a sky-projected spin-orbit angle of λ = –4.9 ± 11.9 deg. In contrast, HAT-P-14b is retrograde, with λ = 189.1 ± 5.1 deg. These results conform with a previously noted pattern among the stellar hosts of close-in giant planets: hotter stars have a wide range of obliquities and cooler stars have low obliquities. This, in turn, suggests that three-body dynamics and tidal dissipation are responsible for the short-period orbits of many exoplanets. In addition, our data revealed a third body in the HAT-P-4 system, which could be a second planet or a companion star.

Additional Information

© 2011 American Astronomical Society. Received 2010 October 6; accepted 2010 December 3; published 2011 January 13. We thank Teruyuki Hirano for interesting discussions related to this work, Amaury Triaud and the anonymous referee for insightful comments on the manuscript, and John Southworth for making available his useful code JKTLD for calculating theoretical limb-darkening coefficients. We gratefully acknowledge support from the NASA Origins program through awards NNX09AD36G and NNX09AB33G, and the MIT Class of 1942. S.A. acknowledges support from an NWO Rubicon fellowship. This paper uses observations obtained with facilities of the Las Cumbres Observatory Global Telescope. Some data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration, and was made possible by the generous financial support of the W.M. Keck Foundation. We extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible. Facilities: Keck:I (HIRES), FLWO:1.2m (KeplerCam), FTN (Spectral)

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