Measurement of the Spin-Orbit Angle of Exoplanet HAT-P-1b
  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, \lambda = 3.7 +/- 2.1 degrees. The small value of \lambda 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. 
John A. Johnson, Joshua N. Winn, Norio Narita, Keigo Enya, Peter K. G.   Williams, Geoffrey W. Marcy, Bun'ei Sato, Yasuhiro ...