We report the discovery by the WASP transit survey of a highly-irradiated , massive ( 2.242 \pm 0.080 M _ { Jup } ) planet which transits a bright ( V = 10.6 ) , evolved F8 star every 2.9 days .
The planet , WASP-71b , is larger than Jupiter ( 1.46 \pm 0.13 R _ { Jup } ) , but less dense ( 0.71 \pm 0.16 \rho _ { Jup } ) .
We also report spectroscopic observations made during transit with the CORALIE spectrograph , which allow us to make a highly-significant detection of the Rossiter-McLaughlin effect .
We determine the sky-projected angle between the stellar-spin and planetary-orbit axes to be \lambda = 20.1 \pm 9.7 degrees , i.e .
the system is ‘ aligned ’ , according to the widely-used alignment criteria that systems are regarded as misaligned only when \lambda is measured to be greater than 10 degrees with 3- \sigma confidence .
WASP-71 , with an effective temperature of 6059 \pm 98 K , therefore fits the previously observed pattern that only stars hotter than 6250 K are host to planets in misaligned orbits .
We emphasise , however , that \lambda is merely the sky-projected obliquity angle ; we are unable to determine whether the stellar-spin and planetary-orbit axes are misaligned along the line-of-sight .
With a mass of 1.56 \pm 0.07 M _ { \odot } , WASP-71 was previously hotter than 6250 K , and therefore might have been significantly misaligned in the past .
If so , the planetary orbit has been realigned , presumably through tidal interactions with the cooling star ’ s growing convective zone .