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Published December 1, 2010 | Published
Journal Article Open

HAT-P-15b: A 10.9 Day Extrasolar Planet Transiting a Solar-type Star


We report the discovery of HAT-P-15b, a transiting extrasolar planet in the "period valley," a relatively sparsely populated period regime of the known extrasolar planets. The host star, GSC 2883-01687, is a G5 dwarf with V = 12.16. It has a mass of 1.01 ± 0.04 M_☉, radius of 1.08 ± 0.04 R_☉, effective temperature 5568 ± 90 K, and metallicity [Fe/H] = +0.22 ± 0.08. The planetary companion orbits the star with a period P = 10.863502 ± 0.000027 days, transit epoch T_c = 2454638.56019 ± 0.00048 (BJD), and transit duration 0.2285 ± 0.0015 days. It has a mass of 1.946 ± 0.066 M_J and radius of 1.072 ± 0.043 R_J yielding a mean density of 1.96 ± 0.22 g cm^(-3). At an age of 6.8^(+2.5))(–1.6) Gyr, the planet is H/He-dominated and theoretical models require about 2% (10 M_⊕) worth of heavy elements to reproduce its measured radius. With an estimated equilibrium temperature of ~820 K during transit, and ~1000 K at occultation, HAT-P-15b is a potential candidate to study moderately cool planetary atmospheres by transmission and occultation spectroscopy.

Additional Information

© 2010 American Astronomical Society. Received 2010 May 24; accepted 2010 August 19; published 2010 November 9. 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. HATNet operations have been funded by NASA grants NNG04GN74G, NNX08AF23G, and SAO IR&D. Work of G.Á.B. and J.A.J. was 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 (programs A285Hr and A146Hr) and NASA (programs N128Hr, N145Hr, and N018Hr). We thank the anonymous referee for the helpful comments concerning the radial velocity dispersion. Note Added in Proof: Three new long-period TEPs have been discovered since the acceptance of this paper: the first double transiting system Kepler-9b,c (Holman et al. 2010) and HAT-P-17b,c with planet 'b' transiting and 'c' causing RV variation (Howard et al. 2010).

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