WASP-47: A Compact Multiplanet System With a hot Jupiter and an Ultra-short Period ExoPlanet

A low stellar obliquity for WASP-47, a compact multiplanet system with a hot Jupiter and an ultra-short period planet

Authors:

Sanchis-Ojeda et al

Abstract:

We have detected the Rossiter-Mclaughlin effect during a transit of WASP-47b, the only known hot Jupiter with close planetary companions. By combining our spectroscopic observations with Kepler photometry, we show that the projected stellar obliquity is λ=0∘±24∘. We can firmly exclude a retrograde orbit for WASP-47b, and rule out strongly misaligned prograde orbits. Low obliquities have also been found for most of the other compact multiplanet systems that have been investigated. The Kepler-56 system, with two close-in gas giants transiting their subgiant host star with an obliquity of at least 45∘, remains the only clear counterexample.