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Orbital Phase Variations of the Eccentric Giant Planet HAT-P-2b

Lewis, Nikole K. and Knutson, Heather A. and Showman, Adam P. and Cowan, Nicolas B. and Laughlin, Gregory and Burrows, Adam and Deming, Drake and Crepp, Justin R. and Mighell, Kenneth J. and Agol, Eric and Bakos, Gáspár Á. and Charbonneau, David and Désert, Jean-Michel and Fischer, Debra A. and Fortney, Jonathan J. and Hartman, Joel D. and Hinkley, Sasha and Howard, Andrew W. and Johnson, John Asher and Kao, Melodie and Langton, Jonathan and Marcy, Geoffrey W. (2013) Orbital Phase Variations of the Eccentric Giant Planet HAT-P-2b. Astrophysical Journal, 766 (2). Art. No. 95. ISSN 0004-637X.

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We present the first secondary eclipse and phase curve observations for the highly eccentric hot Jupiter HAT-P-2b in the 3.6, 4.5, 5.8, and 8.0 μm bands of the Spitzer Space Telescope. The 3.6 and 4.5 μm data sets span an entire orbital period of HAT-P-2b (P = 5.6334729 d), making them the longest continuous phase curve observations obtained to date and the first full-orbit observations of a planet with an eccentricity exceeding 0.2. We present an improved non-parametric method for removing the intrapixel sensitivity variations in Spitzer data at 3.6 and 4.5 μm that robustly maps position-dependent flux variations. We find that the peak in planetary flux occurs at 4.39 ± 0.28, 5.84 ± 0.39, and 4.68 ± 0.37 hr after periapse passage with corresponding maxima in the planet/star flux ratio of 0.1138% ± 0.0089%, 0.1162% ± 0.0080%, and 0.1888% ± 0.0072% in the 3.6, 4.5, and 8.0 μm bands, respectively. Our measured secondary eclipse depths of 0.0996% ± 0.0072%, 0.1031% ± 0.0061%, 0.071%^(+0.029%)_(-0.013%), and 0.1392% ± 0.0095% in the 3.6, 4.5, 5.8, and 8.0 μm bands, respectively, indicate that the planet cools significantly from its peak temperature before we measure the dayside flux during secondary eclipse. We compare our measured secondary eclipse depths to the predictions from a one-dimensional radiative transfer model, which suggests the possible presence of a transient day side inversion in HAT-P-2b's atmosphere near periapse. We also derive improved estimates for the system parameters, including its mass, radius, and orbital ephemeris. Our simultaneous fit to the transit, secondary eclipse, and radial velocity data allows us to determine the eccentricity (e = 0.50910 ± 0.00048) and argument of periapse (ω = 188°.09 ± 0°.39) of HAT-P-2b's orbit with a greater precision than has been achieved for any other eccentric extrasolar planet. We also find evidence for a long-term linear trend in the radial velocity data. This trend suggests the presence of another substellar companion in the HAT-P-2 system, which could have caused HAT-P-2b to migrate inward to its present-day orbit via the Kozai mechanism.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle Paper
Lewis, Nikole K.0000-0002-8507-1304
Knutson, Heather A.0000-0002-0822-3095
Cowan, Nicolas B.0000-0001-6129-5699
Laughlin, Gregory0000-0002-3253-2621
Burrows, Adam0000-0002-3099-5024
Deming, Drake0000-0001-5727-4094
Crepp, Justin R.0000-0003-0800-0593
Agol, Eric0000-0002-0802-9145
Bakos, Gáspár Á.0000-0001-7204-6727
Charbonneau, David0000-0002-9003-484X
Désert, Jean-Michel0000-0002-0875-8401
Fischer, Debra A.0000-0003-2221-0861
Fortney, Jonathan J.0000-0002-9843-4354
Hartman, Joel D.0000-0001-8732-6166
Hinkley, Sasha0000-0001-8074-2562
Howard, Andrew W.0000-0001-8638-0320
Johnson, John Asher0000-0001-9808-7172
Kao, Melodie0000-0001-5125-1414
Marcy, Geoffrey W.0000-0002-2909-0113
Additional Information:© 2013 American Astronomical Society. Received 2012 October 18; accepted 2013 February 19; published 2013 March 13. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by JPL/Caltech. N.K.L. was further supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program (NNX08AX02H), Origins Program (NNX08AF27G), and in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. N.K.L. wishes to thank B. K. Jackson and J. A. Carter for many useful discussions during the preparation of this manuscript and the anonymous referee for their helpful suggestions.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX08AX02H
NASA Exoplanet Science InstituteUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:atmospheric effects; methods: numerical; planets and satellites: general; planets and satellites: individual (HAT-P-2b); techniques: photometric
Issue or Number:2
Record Number:CaltechAUTHORS:20130503-092758220
Persistent URL:
Official Citation:Orbital Phase Variations of the Eccentric Giant Planet HAT-P-2b Nikole K. Lewis et al. 2013 ApJ 766 95
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38255
Deposited By: Ruth Sustaita
Deposited On:03 May 2013 16:54
Last Modified:09 Mar 2020 13:18

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