HAT-P-7: A Retrograde or Polar Orbit, and a Third Body
Abstract
We show that the exoplanet HAT-P-7b has an extremely tilted orbit, with a true angle of at least 86° with respect to its parent star's equatorial plane, and a strong possibility of retrograde motion. We also report evidence for an additional planet or companion star. The evidence for the unparalleled orbit and the third body is based on precise observations of the star's apparent radial velocity (RV). The anomalous RV due to rotation (the Rossiter-McLaughlin effect) was found to be a blueshift during the first half of the transit and a redshift during the second half, an inversion of the usual pattern, implying that the angle between the sky-projected orbital and stellar angular momentum vectors is 182°.5 ± 9°.4. The third body is implicated by excess RV variation of the host star over 2 yr. Some possible explanations for the tilted orbit of HAT-P-7b are a close encounter with another planet, the Kozai effect, and resonant capture by an inward-migrating outer planet.
Additional Information
© 2009 American Astronomical Society. Received 2009 August 12; accepted 2009 August 21; published 2009 September 8. We are grateful to Yasushi Suto and Ed Turner for stimulating our interest in this subject; Norio Narita and his team for sharing their data in advance of publication; Dan Fabrycky, András Pál, Darin Raggozine, Scott Tremaine, Bill Welsh, and the anonymous referee for helpful comments on the manuscript; Akito Tajitsu, Tae-Soo Pyo, Mark Everett, Howard Isaacson, and Zach Gazak for assistance with observing; Gáspár Bakos and Joel Hartman for help obtaining telescope time; Eric Gaidos and Debra Fischer for trading telescope time on short notice; and Hector Balbontin for hospitality at Las Campanas Observatory where this manuscript was written. Some of the 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 wasmade 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. J.A.J. gratefully acknowledges support from the NSF Astronomy and Astrophysics Postdoctoral Fellowship program (grant AST-0702821). S.A. acknowledges the support of the Netherlands Organisation for Scientific Research (NWO). J.N.W. gratefully acknowledges support from the NASA Origins program through awards NNX09AD36G and NNX09AB33G, and from an MIT Class of 1942 Career Development Professorship. Facilities: Subaru (HDS), Keck I (HIRES), FLWO 1.2 m (Keplercam)Attached Files
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Additional details
- Eprint ID
- 36508
- Resolver ID
- CaltechAUTHORS:20130122-104348576
- NSF Astronomy and Astrophysics Fellowship
- AST-0702821
- Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)
- NASA
- NNX09AD36G
- NASA
- NNX09AB33G
- MIT Class of 1942 Career Development Professorship
- Created
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2013-01-23Created from EPrint's datestamp field
- Updated
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2021-11-09Created from EPrint's last_modified field