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_⊙ 1.69_-0.06^+0.11 R_⊙, 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 bis 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_⊙, 2.07_-0.08^+0.19 R_⊙, T_eff = 6036 ± 120 K) every 4.08722 ± 0.00022 days. Despite its high irradiation (~2.3 × 10⁹ erg s^-1 cm^-2), WASP-73 b has a high mean density (1.20_-0.30^+0.26 ρ_Jup) that suggests an enrichment of the planet in heavy elements. The planet WASP-88 bis a 0.56 ± 0.08 M_Juphot Jupiter orbiting a V = 11.4 F6-type star (1.45 ± 0.05 M_⊙, 2.08_-0.06^+0.12 R_⊙, 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.