Measurement of the Spin-Orbit Angle of Exoplanet HAT-P-1b

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

Abstract

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.

Additional Information

© 2008 American Astronomical Society. Received 2008 April 28; accepted 2008 June 9. Based on observations obtained at the Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration; the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; and the Lick Observatory, which is operated by the University of California. We thank the students of GWM's Ay120 Advanced Astronomy Lab course for observing and measuring the transit light curve of HAT-P-1. In particular, we acknowledge the efforts of Kimberly Aller, Niklaus Kemming, Anthony Shu, and Edward Young. We thank the UCO/Lick technical staff for the new remote observing capability, allowing the photometry to be carried out from UC Berkeley. We are grateful for support from the NASA Keck PI Data Analysis Fund (JPL 1326712). J. A. J. and G. B. are NSF Astronomy and Astrophysics Postdoctoral Fellows with support from the NSF grant AST 07-02821. We appreciate funding from NASA grant NNG 05GK92G (to G. W. M.). P. K. G. W. is supported by an NSF Graduate Research Fellowship. This research has made use of the SIMBAD database operated at CDS, Strasbourg, France, and the NASA ADS database. The authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, the Keck and Subaru observations presented herein would not have been possible.

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