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Published December 10, 2009 | Published
Journal Article Open

HAT-P-13b,c: A Transiting Hot Jupiter with a Massive Outer Companion on an Eccentric Orbit


We report on the discovery of a planetary system with a close-in transiting hot Jupiter on a near circular orbit and a massive outer planet on a highly eccentric orbit. The inner planet, HAT-P-13b, transits the bright V = 10.622 G4 dwarf star GSC 3416 – 00543 every P = 2.916260 ± 0.000010 days, with transit epoch T_c = 2454779.92979 ± 0.00038 (BJD) and duration 0.1345 ± 0.0017 days. The outer planet HAT-P-13c orbits the star every P_2 = 428.5 ± 3.0 days with a nominal transit center (assuming zero impact parameter) of T_(2c) = 2454870.4 ± 1.8 (BJD) or time of periastron passage T_(2,peri) = 2454890.05 ± 0.48 (BJD). Transits of the outer planet have not been observed, and may not be present. The host star has a mass of 1.22^(+0.05)_(–0.10) M_☉, radius of 1.56 ± 0.08 R_☉, effective temperature of 5653 ± 90 K, and is rather metal-rich with [Fe/H] = +0.41 ± 0.08. The inner planetary companion has a mass of 0.853^(+0.029)_(–0.046) M_J, and radius of 1.281 ± 0.079 R_J, yielding a mean density of 0.498^(+0.103)_(–0.069) g cm^(–3). The outer companion has m_2 sin i_2 = 15.2 ± 1.0 M_J, and orbits on a highly eccentric orbit of e_2 = 0.691 ± 0.018. While we have not detected significant transit timing variations of HAT-P-13b, due to gravitational and light-travel time effects, future observations will constrain the orbital inclination of HAT-P-13c, along with its mutual inclination to HAT-P-13b. The HAT-P-13 (b, c) double-planet system may prove extremely valuable for theoretical studies of the formation and dynamics of planetary systems.

Additional Information

© 2009 American Astronomical Society. Received 2009 July 20; accepted 2009 October 13; published 2009 November 23. 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, A264Hr) and NASA (N128Hr, N145Hr). 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). We acknowledge partial support also from the Kepler Mission under NASA Cooperative Agreement NCC2-1390 (PI: D.W.L.). G.K. thanks the Hungarian Scientific Research Foundation (OTKA) for support through grant K-60750. G.T. acknowledges partial support from NASA Origins grant NNX09AF59G. This research has made use of Keck telescope time granted through NOAO (program A146Hr,A264Hr) and NASA (N128Hr,N145Hr). We are grateful to Josh Winn and Matthew Holman for their flexibility in swapping nights at the FLWO 1.2 m telescope. We thank the anonymous referee for the useful comments that improved this paper.

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