HAT-P-1 spin-orbit angle measured.

Measurement of the Spin-Orbit Angle of Exoplanet HAT-P-1b
http://arxiv.org/abs/0806.1734

Abstract wrote:

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.

There's lots of good information in there. Updated planet radius and mass values, as well as planet orbital period, and star mass and radius.

Orbit keeps being nearly circular. Not alike HAT-P-2 which is quite eccentric (e=0.5)