WASP-54b, WASP-56b, and WASP-57b: Three new sub-Jupiter mass planets from SuperWASP

International audienceWe present three newly discovered sub-Jupiter mass planets from the SuperWASP survey: WASP-54b is a heavily bloated planet of mass 0.636(-0.024)(+0.025) M-J and radius 1.653(-0.083)(+0.090) R-J. It orbits a F9 star, evolving off the main sequence, every 3.69 days. Our MCMC fit of the system yields a slightly eccentric orbit (e = 0.067(-0.025)(+ 0.033)) for WASP-54b. We investigated further the veracity of our detection of the eccentric orbit for WASP-54b, and we find that it could be real. However, given the brightness of WASP-54 V = 10.42 mag, we encourage observations of a secondary eclipse to draw robust conclusions on both the orbital eccentricity and the thermal structure of the planet. WASP-56b and WASP-57b have masses of 0.571(-0.035)(+ 0.034) M-J and 0.672(-0.046)(+ 0.049) M-J, respectively; and radii of 1.092(-0.033)(+ 0.035) R-J for WASP-56b and 0.916(-0.014)(+0.017) R-J for WASP-57b. They orbit main sequence stars of spectral type G6 every 4.67 and 2.84 days, respectively. WASP-56b and WASP-57b show no radius anomaly and a high density possibly implying a large core of heavy elements; possibly as high as similar to 50 M-circle plus in the case of WASP-57b. However, the composition of the deep interior of exoplanets remains still undetermined. Thus, more exoplanet discoveries such as the ones presented in this paper, are needed to understand and constrain giant planets' physical properties