2011MNRAS.414.3023S

We present observations of the Rossiter–McLaughlin effect for the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b, and deduce the orientations of the planetary orbits with respect to the host stars' rotation axes. The planets WASP-24b, WASP-38b and HAT-P-8b appear to move in prograde orbits and be well aligned, having sky-projected spin-orbit angles consistent with zero: λ=-4{img}7±4{img}0, 15°⁺³³_–43and {img}, respectively. The host stars have T_eff< 6250 K and conform with the trend of cooler stars having low obliquities. WASP-38b is a massive planet on a moderately long period, eccentric orbit so may be expected to have a misaligned orbit given the high obliquities measured in similar systems. However, we find no evidence for a large spin-orbit angle. By contrast, WASP-1b joins the growing number of misaligned systems and has an almost polar orbit, λ={img}. It is neither very massive, eccentric nor orbiting a hot host star, and therefore does not share the properties of many other misaligned systems.

This work is based on observations collected with the SOPHIE spectrograph on the 1.93-m telescope at Observatoire de Haute-Provence (CNRS), France, by the SOPHIE Consortium; the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias and the HARPS spectrograph mounted on the European Southern Observatory (ESO) 3.6-m telescope at the La Silla Observatory in Chile under proposal 084.C-0185.