The Rossiter-McLaughlin effect of the transiting exoplanet XO-4b

Norio Narita, Teruyuki Hirano, Roberto Sanchis-Ojeda, Joshua N. Winn, Matthew J. Holman, Bun'ei Sato, Wako Aoki, Motohide Tamura

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39 Scopus citations


We report photometric and radial velocity observations of the XO-4 transiting planetary system, conducted with the FLWO 1.2 m telescope and the 8.2 m Subaru Telescope. Based on the new light curves, the refined transit ephemeris of XO-4b is P = 4.1250828± 0.0000040d and Tc [BJDTDB] = 2454485.93323± 0.00039.We measured the Rossiter-McLaughlin effect of XO-4b and estimated the sky-projected angle between the stellar spin axis and the planetary orbital axis to be λ = -46° 7+8° 1 -6° 1. This measurement of λ is less robust than in some other cases because the impact parameter of the transit is small, causing a strong degeneracy between λ and the projected stellar rotational velocity. Nevertheless, our finding of a spin-orbit misalignment suggests that the migration process for XO-4b involved few-body dynamics rather than interaction with a gaseous disk. In addition, our result conforms with the pattern reported by Winn et al. (2010, ApJ, 718, L145) that high obliquities are preferentially found for stars with effective temperatures hotter than 6250 K

Original languageEnglish (US)
Pages (from-to)L61-L65
JournalPublications of the Astronomical Society of Japan
Issue number6
StatePublished - Dec 25 2010
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Stars:planetary systems:individual (XO-4)
  • Stars:rotation
  • Techniques:photometric
  • Techniques:radial velocities
  • Techniques:spectroscopic


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