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HAT-P-18b and HAT-P-19b: two low-density saturn-mass planets transiting metal-rich K stars

Hartman, J. D. and Bakos, G. Á. and Sato, B. and Torres, G. and Noyes, R. W. and Latham, D. W. and Kovács, G. and Fischer, D. A. and Howard, A. W. and Johnson, J. A. and Marcy, G. W. and Buchhave, L. A. and Füresz, G. and Perumpilly, G. and Béky, B. and Stefanik, R. P. and Sasselov, D. D. and Esquerdo, G. A. and Everett, M. and Csubry, Z. and Lázár, J. and Papp, I. and Sári, P. (2011) HAT-P-18b and HAT-P-19b: two low-density saturn-mass planets transiting metal-rich K stars. Astrophysical Journal, 726 (1). Art. No. 52. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20110201-101913698

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Abstract

We report the discovery of two new transiting extrasolar planets. HAT-P-18b orbits the V = 12.759 K2 dwarf star GSC 2594−00646, with a period P = 5.508023 ± 0.000006 days, transit epoch T_c = 2454715.02174 ± 0.00020 (BJD), and transit duration 0.1131 ± 0.0009 days. The host star has a mass of 0.77 ± 0.03 M_⊙, radius of 0.75±0.04 R_⊙, effective temperature 4803 ± 80 K, and metallicity [Fe/H] = +0.10 ± 0.08. The planetary companion has 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). HAT-P-19b orbits the V = 12.901 K1 dwarf star GSC 2283−00589, with a period P = 4.008778 ± 0.000006 days, transit epoch T_c = 2455091.53417 ± 0.00034 (BJD), and transit duration 0.1182 ± 0.0014 days. The host star has a mass of 0.84 ± 0.04 M_⊙, radius of 0.82 ± 0.05 R_⊙, effective temperature 4990 ± 130 K, and metallicity [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, yielding a mean density of 0.25±0.04 g cm^(−3). The radial velocity residuals for HAT-P-19 exhibit a linear trend in time, which indicates the presence of a third body in the system. Comparing these observations with theoretical models, we find that HAT-P-18b and HAT-P-19b are each consistent with a hydrogen–heliumdominated gas giant planet with negligible core mass. HAT-P-18b and HAT-P-19b join HAT-P-12b and WASP-21b in an emerging group of low-density Saturn-mass planets, with negligible inferred core masses. However, unlike HAT-P-12b and WASP-21b, both HAT-P-18b and HAT-P-19b orbit stars with super-solar metallicity. This calls into question the heretofore suggestive correlation between the inferred core mass and host star metallicity for Saturn-mass planets.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/726/1/52DOIArticle
http://iopscience.iop.org/0004-637X/726/1/52/PublisherArticle
ORCID:
AuthorORCID
Torres, G.0000-0002-5286-0251
Latham, D. W.0000-0001-9911-7388
Howard, A. W.0000-0001-8638-0320
Marcy, G. W.0000-0002-2909-0113
Buchhave, L. A.0000-0003-1605-5666
Everett, M.0000-0002-0885-7215
Additional Information:© 2011 The American Astronomical Society. Received 2010 July 27; accepted 2010 November 2; published 2010 December 14. 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 (A146Hr, A201Hr, and A264Hr), NASA (N018Hr, N049Hr, N128Hr, and N167Hr), and by the NOAO Keck-Gemini time exchange program (G329Hr). Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based in part on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. HATNet operations have been funded by NASA grants NNG04GN74G, NNX08AF23G and SAO IR&D grants. Work of G.Á.B. and J.A.J. were supported by the Postdoctoral Fellowship of the NSF Astronomy and Astrophysics Program (AST- 0702843 and AST-0702821, respectively). G.T. acknowledges partial support from NASA grant NNX09AF59G. We acknowledge partial support also from the Kepler Mission under NASA Cooperative Agreement NCC2-1390 (D.W.L., PI). G.K. thanks the Hungarian Scientific Research Foundation (OTKA) for support through grant K-81373. This research has made use of Keck telescope time granted through NOAO(programsA146Hr, A201Hr, and A264Hr), NASA (programs N018Hr, N049Hr, N128Hr, and N167Hr), and through the NOAO Keck-Gemini time exchange program (program G329Hr).
Funders:
Funding AgencyGrant Number
National Optical Astronomy Observatory (NOAO)A146Hr
National Optical Astronomy Observatory (NOAO)A201Hr
National Optical Astronomy Observatory (NOAO)A264Hr
National Optical Astronomy Observatory (NOAO)G329Hr
NASAN018Hr
NASAN049Hr
NASAN128Hr
NASAN167Hr
NASANNG04GN74G
NASANNX08AF23G
NASANNX09AF59G
NASANCC2-1390
Smithsonian Astrophysical ObservatoryUNSPECIFIED
NSFAST-0702843
NSFAST-0702821
Hungarian Scientific Research Fund (OTKA)K-81373
Subject Keywords:planetary systems – stars: individual (HAT-P-18, GSC 2594-00646, HAT-P-19, GSC 2283-00589) – techniques: photometric – techniques: spectroscopic
Issue or Number:1
Classification Code:PACS: 97.82.-j; 97.10.Nf; 97.20.Jg; 97.10.Tk; 97.10.Wn; 97.10.Ri
Record Number:CaltechAUTHORS:20110201-101913698
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20110201-101913698
Official Citation:J. D. Hartman et al. 2011 ApJ 726 52 doi: 10.1088/0004-637X/726/1/52
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21949
Collection:CaltechAUTHORS
Deposited By: Benjamin Perez
Deposited On:01 Feb 2011 21:10
Last Modified:03 Oct 2019 02:32

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