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HAT-P-12b: A Low-Density Sub-Saturn Mass Planet Transiting a Metal-Poor K Dwarf

Hartmann, J. D. and Bakos, G. Á. and Torres, G. and Kovács, Géza and Noyes, R. W. and Pál, A. and Latham, D. W. and Sipőcz, B. and Fischer, D. A. and Johnson, J. A. and Marcy, G. W. and Butler, R. P. and Howard, A. W. and Esquerdo, G. A. and Sasselov, D. D. and Kovács, Gábor and Stefanik, R. P. and Fernandez, J. M. and Lázár, J. and Papp, I. and Sári, P. (2009) HAT-P-12b: A Low-Density Sub-Saturn Mass Planet Transiting a Metal-Poor K Dwarf. Astrophysical Journal, 706 (1). pp. 785-796. ISSN 0004-637X.

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We report on the discovery of HAT-P-12b, a transiting extrasolar planet orbiting the moderately bright V ≈ 12.8 K4 dwarf GSC 03033 – 00706, with a period P = 3.2130598 ± 0.0000021 d, transit epoch T_c = 2454419.19556 ± 0.00020 (BJD), and transit duration 0.0974 ± 0.0006 d. The host star has a mass of 0.73 ± 0.02 M_☉, radius of 0.70^(+0.02)_(–0.01) R_☉, effective temperature 4650 ± 60 K, and metallicity [Fe/H] = –0.29 ± 0.05. We find a slight correlation between the observed spectral line bisector spans and the radial velocity, so we consider, and rule out, various blend configurations including a blend with a background eclipsing binary, and hierarchical triple systems where the eclipsing body is a star or a planet. We conclude that a model consisting of a single star with a transiting planet best fits the observations, and show that a likely explanation for the apparent correlation is contamination from scattered moonlight. Based on this model, the planetary companion has a mass of 0.211 ± 0.012 M_J and radius of 0.959^(+0.029)_(–0.021) R_J yielding a mean density of 0.295 ± 0.025 g cm^(–3). Comparing these observations with recent theoretical models, we find that HAT-P-12b is consistent with a ~1-4.5 Gyr, mildly irradiated, H/He-dominated planet with a core mass M_C ≾ 10 M_⊕. HAT-P-12b is thus the least massive H/He-dominated gas giant planet found to date. This record was previously held by Saturn.

Item Type:Article
Related URLs:
URLURL TypeDescription
Bakos, G. Á.0000-0001-7204-6727
Torres, G.0000-0002-5286-0251
Latham, D. W.0000-0001-9911-7388
Fischer, D. A.0000-0003-2221-0861
Johnson, J. A.0000-0001-9808-7172
Marcy, G. W.0000-0002-2909-0113
Howard, A. W.0000-0001-8638-0320
Esquerdo, G. A.0000-0002-9789-5474
Sasselov, D. D.0000-0001-7014-1771
Additional Information:© 2009 American Astronomical Society. Received 2009 April 29; accepted 2009 October 13; published 2009 November 5. 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 (A264Hr, A146Hr) and NASA (N162Hr, N128Hr). We thank the referee, Peter McCullough, for several suggestions that improved the quality of this paper, and Scott Gaudi for a helpful discussion. HATNet operations have been funded by NASA grants NNG04GN74G, NNX08AF23G, and SAO IR&D grants. Work of G.Á.B. and J. Johnson were supported by the Postdoctoral Fellowship of the NSF Astronomy and Astrophysics Program (AST-0702843 and AST-0702821, respectively). 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-60750. This research has made use of Keck telescope time granted through NOAO and NASA. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.
Funding AgencyGrant Number
Smithsonian Astrophysical ObservatoryUNSPECIFIED
NSF Astronomy and Astrophysics FellowshipAST-0702843
NSF Astronomy and Astrophysics FellowshipAST-0702821
Hungarian Scientific Research Fund (OTKA)K-60750
Subject Keywords:planetary systems; stars: individual (HAT-P-12, GSC 03033 – 00706); techniques: photometric; techniques: spectroscopic
Issue or Number:1
Record Number:CaltechAUTHORS:20130114-090013213
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Official Citation:HAT-P-12b: A Low-Density Sub-Saturn Mass Planet Transiting a Metal-Poor K Dwarf J. D. Hartman et al. 2009 ApJ 706 785
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36343
Deposited By: Ruth Sustaita
Deposited On:14 Jan 2013 17:37
Last Modified:09 Mar 2020 13:19

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