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

Creators: Hartmann, J. D.; Bakos, G. Á.; Torres, G.; Kovács, Géza; Noyes, R. W.; Pál, A.; Latham, D. W.; Sipőcz, B.; Fischer, D. A.; Johnson, J. A.; Marcy, G. W.; Butler, R. P.; Howard, A. W.; Esquerdo, G. A.; Sasselov, D. D.; Kovács, Gábor; Stefanik, R. P.; Fernandez, J. M.; Lázár, J.; Papp, I.; Sári, P.

Abstract

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.

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.

Attached Files

Published - 0004-637X_706_1_785.pdf

Files

0004-637X_706_1_785.pdf

Files (931.6 kB)

Name	Size	Download all
0004-637X_706_1_785.pdf md5:d9e8a26f5005ae0e15ffc611acba33a6	931.6 kB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes