A high stellar obliquity in the WASP-7 exoplanetary system

Simon Albrecht, Joshua N. Winn, R. Paul Butler, Jeffrey D. Crane, Stephen A. Shectman, Ian B. Thompson, Teruyuki Hirano, Robert A. Wittenmyer

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We measure a tilt of 86° ± 6° between the sky projections of the rotation axis of the WASP-7 star and the orbital axis of its close-in giant planet. This measurement is based on observations of the Rossiter-McLaughlin (RM) effect with the Planet Finder Spectrograph on the Magellan II telescope. The result conforms with the previously noted pattern among hot-Jupiter hosts, namely, that the hosts lacking thick convective envelopes have high obliquities. Because the planet's trajectory crosses a wide range of stellar latitudes, observations of the RM effect can in principle reveal the stellar differential rotation profile; however, with the present data the signal of differential rotation could not be detected. The host star is found to exhibit radial-velocity noise ("stellar jitter") with an amplitude of ≈ 30 m s-1 over a timescale of days.

Original languageEnglish (US)
Article number189
JournalAstrophysical Journal
Issue number2
StatePublished - Jan 10 2012
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • planetary systems
  • planets and satellites: formation
  • planetstar interactions
  • stars: individual (WASP-7)
  • stars: rotation
  • techniques: spectroscopic


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