HAT-P-20b-HAT-P-23b: FOUR MASSIVE TRANSITING EXTRASOLAR PLANETS

We report the discovery of four relatively massive (2-7M(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-circle dot, radius of 0.69 +/- 0.02 R-circle dot, 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-circle dot, radius of 1.10 +/- 0.08 R-circle dot, 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(-0.99)(+1.59) 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-circle dot, radius of 1.04 +/- 0.04 R-circle dot, 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(-0.29)(+0.40) 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-circle dot, radius of 1.20 +/- 0.07 R-circle dot, 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(-1.8)(+2.9) Myr) before it gets engulfed by the star.