Starspots and spin-orbit alignment in the WASP-4 exoplanetary system

Roberto Sanchis-Ojeda, Joshua N. Winn, Matthew J. Holman, Joshua A. Carter, David J. Osip, Cesar I. Fuentes

Research output: Chapter in Book/Report/Conference proceedingConference contribution


We present the photometric analysis of 4 transits of the exoplanet WASP-4b, obtained with the Baade 6.5m telescope, one of the two Magellan telescopes at Las Campanas. The light curves have a photometric precision of 0.5 mmag and a time sampling of 30s. This high precision has allowed us to detect several "spot anomalies": temporary brightenings due to the occultation of a starspot on the transit chord. By analyzing these anomalies we find the sky-projected stellar obliquity to be λ = 1°+12°-14°. The small value suggests that the planet migration mechanism preserved the initially low obliquity, or that tidal evolution has realigned the system.

Original languageEnglish (US)
Title of host publicationThe Astrophysics of Planetary Systems
Subtitle of host publicationFormation, Structure, and Dynamical Evolution
EditorsAlessandro Sozzetti, Mario Lattanzi, Alan Boss
Number of pages2
StatePublished - Oct 2010
Externally publishedYes

Publication series

NameProceedings of the International Astronomical Union
ISSN (Print)1743-9213
ISSN (Electronic)1743-9221

All Science Journal Classification (ASJC) codes

  • Medicine (miscellaneous)
  • Astronomy and Astrophysics
  • Nutrition and Dietetics
  • Public Health, Environmental and Occupational Health
  • Space and Planetary Science


  • Planetary systems
  • Stars: spots
  • Techniques: photometric


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