Mass of WASP-33b

We analysed an extended time series of high-resolution spectra of the δSct star WASP-33 with the aim to determine the effect of its planet WASP-33b. We found ten frequencies in the measured radial velocities. Three of them we can attribute to previously observed photometric oscillations due to non-radial pulsations. One frequency exactly agrees with the orbital period of the planet. The semiamplitude of the corresponding variation is 304 ± 20 m s−1. This finding allows us to give a new estimate of the mass of WASP-33b of 2.1 ± 0.2 Jupiter masses. Its mean density probably is at least 0.6 g cm−3, a value that can be expected for a planet of its mass that orbits an A-type star in 1.22 d.