Measurement of the spin-orbit angle of exoplanet HAT-P-1b

John Asher Johnson, Joshua N. Winn, Norio Narita, Keigo Enya, Peter K.G. Williams, Geoffrey W. Marcy, Bun'ei Sato, Yasuhiro Ohta, Atsushi Taruya, Yasushi Suto, Edwin L. Turner, Gaspar Bakos, R. Paul Butler, Steven S. Vogt, Wako Aoki, Motohide Tamura, Toru Yamada, Yuzuru Yoshii, Marton Hidas

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


We present new spectroscopic and photometric observations of the HAT-P-1 planetary system. Spectra obtained during three transits exhibit the Rossiter-McLaughlin effect, allowing us to measure the angle between the sky projections of the stellar spin axis and orbit normal, λ = 3.7° ±2.1°. The small value of λ for this and other systems suggests that the dominant planet migration mechanism preserves spin-orbit alignment. Using two new transit light curves, we refine the transit ephemeris and reduce the uncertainty in the orbital period by an order of magnitude. We find a upper limit on the orbital eccentricity of 0.067, with 99% confidence, by combining our new radial velocity measurements with those obtained previously.

Original languageEnglish (US)
Pages (from-to)649-657
Number of pages9
JournalAstrophysical Journal
Issue number1
StatePublished - Oct 10 2008

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Planetary systems: formation
  • Stars: individual (ADS 16402a, HAT-P-1)
  • Techniques: radial velocities


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