Transiting planets from WASP-South, Euler, and TRAPPIST WASP-68 b, WASP-73 b, and WASP-88 b, three hot Jupiters transiting evolved solar-type stars

Using the WASP transit survey, we report the discovery of three new hot Jupiters, WASP-68 b, WASP-73 b and WASP-88 b. The planet WASP-68 b has a mass of 0.95 +/- 0.03 M-Jup, a radius of 1.24(-0.06)(+0.10) R-Jup, and orbits a V = 10.7 G0-type star (1.24 +/- 0.03 M-circle dot, 1.69(-0.06)(+0.11) R-circle dot, T-eff = 5911 +/- 60 K) with a period of 5.084298 +/- 0.000015 days. Its size is typical of hot Jupiters with similar masses. The planet WASP-73 b is significantly more massive (1.88(-0.06)(+0.07) M-Jup) and slightly larger (1.16(-0.08)(+0.12) R-Jup) than Jupiter. It orbits a V = 10.5 F9-type star (1.34(-0.04)(+0.05) M-circle dot, 2.07(-0.08)(+0.19) R-circle dot, T-eff = 6036 +/- 120 K) every 4.08722 +/- 0.00022 days. Despite its high irradiation (similar to 2.3 x 10(9) erg s(-1) cm(-2)), WASP-73 b has a high mean density (1.20(-0.30)(+0.26) rho(Jup)) that suggests an enrichment of the planet in heavy elements. The planet WASP-88 b is a 0.56 +/- 0.08 M-Jup hot Jupiter orbiting a V = 11.4 F6-type star (1.45 +/- 0.05 M circle dot, 2.08-(+0.12)(0.06) R-circle dot, T-eff = 6431 +/- 130 K) with a period of 4.954000 +/- 0.000019 days. With a radius of 1.70(-0.07)(+0.13) R-Jup, it joins the handful of planets with super-inflated radii. The ranges of ages we determine through stellar evolution modeling are 4.5-7.0 Gyr for WASP-68, 2.8-5.7 Gyr for WASP-73 and 1.8-4.3 Gyr for WASP-88. The star WASP-73 appears to be significantly evolved, close to or already in the subgiant phase. The stars WASP-68 and WASP-88 are less evolved, although in an advanced stage of core H-burning.