HAT-P-20b-HAT-P-23b: Four Massive Transiting Extrasolar Planets

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.

Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Keck time has been granted by NOAO and NASA.