WASP-180Ab: Doppler tomography of a hot Jupiter orbiting the primary star in a visual binary

We report the discovery and characterization of WASP-180Ab, a hot Jupiter confirmed by the detection of its Doppler shadow and by measuring its mass using radial velocities. We find the 0.9 ± 0.1 M_Jup, 1.24 ± 0.04 R_Jup planet to be in a misaligned, retrograde orbit around an F7 star with T_eff = 6500 K and a moderate rotation speed of vsin i_⋆ = 19.9 km s^-1. The host star is the primary of a V = 10.7 binary, where a secondary separated by ∼5 arcsec (∼1200 au) contributes ∼ 30 per cent of the light. WASP-180Ab therefore adds to a small sample of transiting hot Jupiters known in binary systems. A 4.6-d modulation seen in the WASP data is likely to be the rotational modulation of the companion star, WASP-180B.