HAT-P-7: A retrograde or polar orbit, and a third body

Joshua N. Winn, John Asher Johnson, Simon Albrecht, Andrew W. Howard, Geoffrey W. Marcy, Ian J. Crossfield, Matthew J. Holman

Research output: Contribution to journalArticlepeer-review

188 Scopus citations


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 182̇°5 ± 9̇°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.

Original languageEnglish (US)
Pages (from-to)L99-L103
JournalAstrophysical Journal
Issue number2 PART 2
StatePublished - 2009
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Planetary systems
  • Planetary systems: formation
  • Stars: individual (HAT-P-7)
  • Stars: rotation Online-only material: machine-readable table


Dive into the research topics of 'HAT-P-7: A retrograde or polar orbit, and a third body'. Together they form a unique fingerprint.

Cite this