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HAT-P-18b AND HAT-P-19b: TWO LOW-DENSITY SATURN-MASS PLANETS TRANSITING METAL-RICH K STARS

J. D. HartmanHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]G. Á. BakosHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]B. SatoGlobal Edge Institute, Tokyo Institute of Technology, Tokyo, JapanG. TorresHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]R. W. NoyesHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]D. W. LathamHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]G. KovácsKonkoly Observatory, Budapest, HungaryD. A. FischerDepartment of Physics and Astronomy, San Francisco State University, San Francisco, CA, USAA. W. HowardDepartment of Astronomy, University of California, Berkeley, CA, USAJ. A. JohnsonDepartment of Astrophysics, and NASA Exoplanet Science Institute, California Institute of Technology, Pasadena, CA, USAG. W. MarcyDepartment of Astronomy, University of California, Berkeley, CA, USAL. A. BuchhaveHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]G. FüreszHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]G. PerumpillyDepartment of Physics, University of South Dakota, Vermillion, SD, USAB. BékyHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]R. P. StefanikHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]D. D. SasselovHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]G. A. EsquerdoHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]M. EverettHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]Z. CsubryHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA; [email protected]J. LázárHungarian Astronomical Association, Budapest, HungaryI. PappHungarian Astronomical Association, Budapest, HungaryP. SáriHungarian Astronomical Association, Budapest, Hungary

2010en

ABI

Annotatsiya

We report the discovery of two new transiting extrasolar planets. HAT-P-18b orbits the V = 12.759 K2 dwarf star\nGSC 2594−00646, with a period P = 5.508023 ± 0.000006 days, transit epoch T_c = 2454715.02174 ± 0.00020\n(BJD), and transit duration 0.1131 ± 0.0009 days. The host star has a mass of 0.77 ± 0.03 M_⊙, radius of\n0.75±0.04 R_⊙, effective temperature 4803 ± 80 K, and metallicity [Fe/H] = +0.10 ± 0.08. The planetary companion\nhas a mass of 0.197±0.013 M_J and radius of 0.995 ± 0.052 R_J, yielding a mean density of 0.25 ± 0.04 g cm^(−3).\nHAT-P-19b orbits the V = 12.901 K1 dwarf star GSC 2283−00589, with a period P = 4.008778 ± 0.000006 days,\ntransit epoch T_c = 2455091.53417 ± 0.00034 (BJD), and transit duration 0.1182 ± 0.0014 days. The host star\nhas a mass of 0.84 ± 0.04 M_⊙, radius of 0.82 ± 0.05 R_⊙, effective temperature 4990 ± 130 K, and metallicity\n[Fe/H] = +0.23 ± 0.08. The planetary companion has a mass of 0.292 ± 0.018 M_J and radius of 1.132 ± 0.072 R_J,\nyielding a mean density of 0.25±0.04 g cm^(−3). The radial velocity residuals for HAT-P-19 exhibit a linear\ntrend in time, which indicates the presence of a third body in the system. Comparing these observations\nwith theoretical models, we find that HAT-P-18b and HAT-P-19b are each consistent with a hydrogen–heliumdominated\ngas giant planet with negligible core mass. HAT-P-18b and HAT-P-19b join HAT-P-12b\nand WASP-21b in an emerging group of low-density Saturn-mass planets, with negligible inferred core masses.\nHowever, unlike HAT-P-12b and WASP-21b, both HAT-P-18b and HAT-P-19b orbit stars with super-solar metallicity.\nThis calls into question the heretofore suggestive correlation between the inferred core mass and host star\nmetallicity for Saturn-mass planets.

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DOI: 10.1088/0004-637x/726/1/52

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