The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b from Rossiter-McLaughlin observations

Simpson, E. K. ; Pollacco, D. ; Cameron, A. Collier ; Hébrard, G. ; Anderson, D. R. ; Barros, S. C. C. ; Boisse, I. ; Bouchy, F. ; Faedi, F. ; Gillon, M. ; Hebb, L. ; Keenan, F. P. ; Miller, G. R. M. ; Moutou, C. ; Queloz, D. ; Skillen, I. ; Sorensen, P. ; Stempels, H. C. ; Triaud, A. ; Watson, C. A. ; Wilson, P. A.

In: Monthly Notices of the Royal Astronomical Society, 2011, vol. 414, no. 4, p. 3023-3035

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    Summary
    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°.7 ± 4°.0, 15°+33−43 and , respectively. The host stars have Teff < 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=. It is neither very massive, eccentric nor orbiting a hot host star, and therefore does not share the properties of many other misaligned systems