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3.6 and 4.5 μm Phase Curves and Evidence for Non-equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b

Knutson, Heather A. and Lewis, Nikole and Fortney, Jonathan J. and Burrows, Adam and Showman, Adam P. and Cowan, Nicolas B. and Agol, Eric and Aigrain, Suzanne and Charbonneau, David and Deming, Drake and Désert, Jean-Michel and Henry, Gregory W. and Langton, Jonathan and Laughlin, Gregory (2012) 3.6 and 4.5 μm Phase Curves and Evidence for Non-equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b. Astrophysical Journal, 754 (1). Art. No. 22. ISSN 0004-637X.

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We present new, full-orbit observations of the infrared phase variations of the canonical hot Jupiter HD 189733b obtained in the 3.6 and 4.5 μm bands using the Spitzer Space Telescope. When combined with previous phase curve observations at 8.0 and 24 μm, these data allow us to characterize the exoplanet's emission spectrum as a function of planetary longitude and to search for local variations in its vertical thermal profile and atmospheric composition. We utilize an improved method for removing the effects of intrapixel sensitivity variations and robustly extracting phase curve signals from these data, and we calculate our best-fit parameters and uncertainties using a wavelet-based Markov Chain Monte Carlo analysis that accounts for the presence of time-correlated noise in our data. We measure a phase curve amplitude of 0.1242% ± 0.0061% in the 3.6 μm band and 0.0982% ± 0.0089% in the 4.5 μm band, corresponding to brightness temperature contrasts of 503 ± 21 K and 264 ± 24 K, respectively. We find that the times of minimum and maximum flux occur several hours earlier than predicted for an atmosphere in radiative equilibrium, consistent with the eastward advection of gas by an equatorial super-rotating jet. The locations of the flux minima in our new data differ from our previous observations at 8 μm, and we present new evidence indicating that the flux minimum observed in the 8 μm is likely caused by an overshooting effect in the 8 μm array. We obtain improved estimates for HD 189733b's dayside planet-star flux ratio of 0.1466% ± 0.0040% in the 3.6 μm band and 0.1787% ± 0.0038% in the 4.5 μm band, corresponding to brightness temperatures of 1328 ± 11 K and 1192 ± 9 K, respectively; these are the most accurate secondary eclipse depths obtained to date for an extrasolar planet. We compare our new dayside and nightside spectra for HD 189733b to the predictions of one-dimensional radiative transfer models from Burrows et al. and conclude that fits to this planet's dayside spectrum provide a reasonably accurate estimate of the amount of energy transported to the night side. Our 3.6 and 4.5 μm phase curves are generally in good agreement with the predictions of general circulation models for this planet from Showman et al., although we require either excess drag or slower rotation rates in order to match the locations of the measured maxima and minima in the 4.5, 8.0, and 24 μm bands. We find that HD 189733b's 4.5 μm nightside flux is 3.3σ smaller than predicted by these models, which assume that the chemistry is in local thermal equilibrium. We conclude that this discrepancy is best explained by vertical mixing, which should lead to an excess of CO and correspondingly enhanced 4.5 μm absorption in this region. This result is consistent with our constraints on the planet's transmission spectrum, which also suggest excess absorption in the 4.5 μm band at the day-night terminator.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Knutson, Heather A.0000-0002-0822-3095
Lewis, Nikole0000-0002-8507-1304
Fortney, Jonathan J.0000-0002-9843-4354
Burrows, Adam0000-0002-3099-5024
Cowan, Nicolas B.0000-0001-6129-5699
Agol, Eric0000-0002-0802-9145
Aigrain, Suzanne0000-0003-1453-0574
Charbonneau, David0000-0002-9003-484X
Deming, Drake0000-0001-5727-4094
Désert, Jean-Michel0000-0002-0875-8401
Henry, Gregory W.0000-0003-4155-8513
Laughlin, Gregory0000-0002-3253-2621
Additional Information:© 2012 The American Astronomical Society. Received 2012 February 22; accepted 2012 May 5; published 2012 June 29. We thank Josh Carter for his assistance in implementing a wavelet MCMC analysis for these data. 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 NASA through an award issued by JPL/Caltech. H.A.K. was supported in part by a fellowship from the Miller Institute for Basic Research in Science.
Funding AgencyGrant Number
Miller Institute for Basic Research in ScienceUNSPECIFIED
Subject Keywords:binaries: eclipsing; planetary systems; techniques: photometric
Issue or Number:1
Record Number:CaltechAUTHORS:20120807-121059996
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Official Citation:3.6 and 4.5 μm Phase Curves and Evidence for Non-equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b Heather A. Knutson et al. 2012 ApJ 754 22
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32982
Deposited By: Aucoeur Ngo
Deposited On:07 Aug 2012 20:12
Last Modified:09 Mar 2020 13:18

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