  We present the measured projected obliquity -- the sky-projected angle
between the stellar spin axis and orbital angular momentum -- of the inner
planet of the HAT-P-17 multi-planet system. We measure the sky-projected
obliquity of the star to be \lambda=19+/-15 degrees by modeling the
Rossiter-McLaughlin (RM) effect in Keck/HIRES radial velocities (RVs). The
anomalous RV time series shows an asymmetry relative to the midtransit time,
ordinarily suggesting a nonzero obliquity -- but in this case at least part of
the asymmetry may be due to the convective blueshift, increasing the
uncertainty in the determination of \lambda. We employ the semi-analytical
approach of Hirano et al. (2011) that includes the effects of macroturbulence,
instrumental broadening, and convective blueshift to accurately model the
anomaly in the net RV caused by the planet eclipsing part of the rotating star.
Obliquity measurements are an important tool for testing theories of planet
formation and migration. To date, the measured obliquities of ~50 Jovian
planets span the full range, from prograde to retrograde, with planets orbiting
cool stars preferentially showing alignment of stellar spins and planetary
orbits. Our results are consistent with this pattern emerging from tidal
interactions in the convective envelopes of cool stars and close-in planets. In
addition, our 1.8 years of new RVs for this system show that the orbit of the
outer planet is more poorly constrained than previously thought, with an
orbital period now in the range of 10-36 years.
