WASP-189b: an ultra-hot Jupiter transiting the bright A star HR 5599 in a polar orbit

We report the discovery of WASP-189b: an ultra-hot Jupiter in a 2.72-d transiting orbit around the $V = 6.6$ A star WASP-189 (HR 5599). We detected periodic dimmings in the stars lightcurve, first with the WASP-South survey facility then with the TRAPPIST-South telescope. We confirmed that a planet is the cause of those dimmings via line-profile tomography and radial-velocity measurements using the HARPS and CORALIE spectrographs. Those reveal WASP-189b to be an ultra-hot Jupiter ($M_{rm P}$ = 2.13 $pm$ 0.28 $M_{rm Jup}$; $R_{rm P}$ = 1.374 $pm$ 0.082 $R_{rm Jup}$) in a polar orbit ($lambda = 89.3 pm 1.4^circ$; $Psi = 90.0 pm 5.8^circ$) around a rapidly rotating A6IV-V star ($T_{rm eff}$ = 8000 $pm$ 100 K; $v_* sin i_*$ $approx$ 100 km, s$^{-1}$). We calculate a predicted equilibrium temperature of $T_{rm eql}$ = 2641 $pm$ 34 K, assuming zero albedo and efficient redistribution, which is the third hottest for the known exoplanets. WASP-189 is the brightest known host of a transiting hot Jupiter and the third-brightest known host of any transiting exoplanet. We note that of the eight hot-Jupiter systems with $T_{rm eff}$ $>$ 7000 K, seven have strongly misaligned orbits, and two of the three systems with $T_{rm eff}$ $geq$ 8000 K have polar orbits (the third is aligned).