Exoplanetary System WASP - 3 : the Projected Spin - Orbit Angle and Evidence for Stellar Activity

In this thesis, I present new spectroscopic and photometric observations of WASP-3, a transiting extrasolar planetary system. From spectra obtained during two transits, I use the Rossiter-McLaughlin effect in a simplified physical model to determine the projected spin-orbit angle between the planetary orbital axis and the stellar rotation axis, A = 2 .91 4 degrees. I use the new photometric data to refine the system parameters. Additionally, I present evidence for stellar activity, as the spectra obtained on UT June 19, 2008 reveal an increase in radial velocity to a peak magnitude of 75 m s1 larger than the expected orbital velocity. Such an anomaly was not observed during a subsequent transit. I find that a good fit to the radial velocity measurements requires omitting the anomalous data and adding a large stellar jitter of 11 m s 1 to the measurement uncertainties. The resulting planetary mass, Mp = 2.14:006 MJ differs from previously reported measurements which found Mp = 1.76-0. M . Together, these observations provide evidence for a region of stellar activity on WASP-3, and the observed anomaly suggests that material in this region exhibited a coherent horizontal motion of appoximately 10 km s-' across the stellar surface at the limb. Thesis Supervisor: Professor Joshua N. Winn Title: Department of Physics