A Caltech Library Service

HAT-P-7: A Retrograde or Polar Orbit, and a Third Body

Winn, Joshua N. and Johson, John Asher and Albrecht, Simon and Howard, Andrew W. and Marcy, Geoffrey W. and Crossfield, Ian J. and Holman, Matthew J. (2009) HAT-P-7: A Retrograde or Polar Orbit, and a Third Body. Astrophysical Journal Letters, 703 (2). L99-L103. ISSN 2041-8205.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Winn, Joshua N.0000-0002-4265-047X
Johson, John Asher0000-0001-9808-7172
Howard, Andrew W.0000-0001-8638-0320
Marcy, Geoffrey W.0000-0002-2909-0113
Crossfield, Ian J.0000-0002-1835-1891
Holman, Matthew J.0000-0002-1139-4880
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)
Funding AgencyGrant Number
NSF Astronomy and Astrophysics FellowshipAST-0702821
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
MIT Class of 1942 Career Development ProfessorshipUNSPECIFIED
Subject Keywords:planetary systems; planetary systems: formation; stars: individual (HAT-P-7); stars: rotation
Issue or Number:2
Record Number:CaltechAUTHORS:20130122-104348576
Persistent URL:
Official Citation:HAT-P-7: A Retrograde or Polar Orbit, and a Third Body Joshua N. Winn et al. 2009 ApJ 703 L99
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36508
Deposited By: Jason Perez
Deposited On:23 Jan 2013 15:20
Last Modified:09 Mar 2020 13:18

Repository Staff Only: item control page