Keywords

We report the discovery of four relatively massive (2–7 M_J) transiting extrasolar planets. HAT-P-20b orbits the moderately bright V = 11.339 K3 dwarf star GSC 1910-00239 on a circular orbit, with a period P = 2.875317  ±  0.000004 days, transit epoch T_c = 2455080.92661  ±  0.00021 (BJD_UTC), and transit duration 0.0770  ±  0.0008 days. The host star has a mass of 0.76  ±  0.03 M_☉, radius of 0.69  ±  0.02 R_☉, effective temperature 4595  ±  80 K, and metallicity [Fe/H] = +0.35  ±  0.08. The planetary companion has a mass of 7.246  ±  0.187 M_J and a radius of 0.867  ±  0.033 R_J yielding a mean density of 13.78  ±  1.50 g cm⁻³. HAT-P-21b orbits the V = 11.685 G3 dwarf star GSC 3013-01229 on an eccentric (e = 0.228  ±  0.016) orbit, with a period P = 4.124481  ±  0.000007 days, transit epoch T_c = 2454996.41312  ±  0.00069, and transit duration 0.1530  ±  0.0027 days. The host star has a mass of 0.95  ±  0.04 M_☉, radius of 1.10  ±  0.08 R_☉, effective temperature 5588  ±  80 K, and metallicity [Fe/H] = +0.01  ±  0.08. The planetary companion has a mass of 4.063  ±  0.161 M_J and a radius of 1.024  ±  0.092 R_J yielding a mean density of 4.68^+1.59_{− 0.99} g cm⁻³. HAT-P-21b is a borderline object between the pM and pL class planets, and the transits occur near apastron. HAT-P-22b orbits the bright V = 9.732 G5 dwarf star HD 233731 on a circular orbit, with a period P = 3.212220  ±  0.000009 days, transit epoch T_c = 2454930.22001  ±  0.00025, and transit duration 0.1196  ±  0.0014 days. The host star has a mass of 0.92  ±  0.03 M_☉, radius of 1.04  ±  0.04 R_☉, effective temperature 5302  ±  80 K, and metallicity [Fe/H] = +0.24  ±  0.08. The planet has a mass of 2.147  ±  0.061 M_J and a compact radius of 1.080  ±  0.058 R_J yielding a mean density of 2.11^+0.40_{− 0.29} g cm⁻³. The host star also harbors an M-dwarf companion at a wide separation. Finally, HAT-P-23b orbits the V = 12.432 G0 dwarf star GSC 1632-01396 on a close to circular orbit, with a period P = 1.212884  ±  0.000002 days, transit epoch T_c = 2454852.26464  ±  0.00018, and transit duration 0.0908  ±  0.0007 days. The host star has a mass of 1.13  ±  0.04 M_☉, radius of 1.20  ±  0.07 R_☉, effective temperature 5905  ±  80 K, and metallicity [Fe/H] = +0.15  ±  0.04. The planetary companion has a mass of 2.090  ±  0.111 M_J and a radius of 1.368  ±  0.090 R_J yielding a mean density of 1.01  ±  0.18 g cm⁻³. HAT-P-23b is an inflated and massive hot Jupiter on a very short period orbit, and has one of the shortest characteristic infall times (7.5^+2.9_{− 1.8} Myr) before it gets engulfed by the star.