3.6 AND 4.5 {mu}m PHASE CURVES AND EVIDENCE FOR NON-EQUILIBRIUM CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HD 189733b

Journal Article · Fri Jul 20 00:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/754/1/22· OSTI ID:22039334

Knutson, Heather A ^[1]; Lewis, Nikole; Showman, Adam P ^[2]; Fortney, Jonathan J; Laughlin, Gregory ^[3]; Burrows, Adam ^[4]; Cowan, Nicolas B ^[5]; Agol, Eric ^[6]; Aigrain, Suzanne ^[7]; Charbonneau, David; Desert, Jean-Michel ^[8]; Deming, Drake ^[9]; Henry, Gregory W ^[10]; Langton, Jonathan ^[11]

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1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States)
2. Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)
3. Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
4. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
5. CIERA, Northwestern University, Evanston, IL 60208 (United States)
6. Department of Astronomy, University of Washington, Seattle, WA 98195 (United States)
7. Sub-department of Astrophysics, Department of Physics, University of Oxford, Oxford OX1 3RH (United Kingdom)
8. Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)
9. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
10. Center of Excellence in Information Systems, Tennessee State University, 3500 John A. Merritt Blvd., Box 9501, Nashville, TN 37209 (United States)
11. Department of Physics, Principia College, 1 Maybeck Place, Elsah, IL 62028 (United States)

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 {mu}m bands using the Spitzer Space Telescope. When combined with previous phase curve observations at 8.0 and 24 {mu}m, 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 {mu}m band and 0.0982% {+-} 0.0089% in the 4.5 {mu}m 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 {mu}m, and we present new evidence indicating that the flux minimum observed in the 8 {mu}m is likely caused by an overshooting effect in the 8 {mu}m array. We obtain improved estimates for HD 189733b's dayside planet-star flux ratio of 0.1466% {+-} 0.0040% in the 3.6 {mu}m band and 0.1787% {+-} 0.0038% in the 4.5 {mu}m 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 {mu}m 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 {mu}m bands. We find that HD 189733b's 4.5 {mu}m nightside flux is 3.3{sigma} 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 {mu}m 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 {mu}m band at the day-night terminator.

• OSTI ID: 22039334
• Journal Information: Astrophysical Journal, Vol. 754, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTRONOMY
ASTROPHYSICS
BRIGHTNESS
CARBON MONOXIDE
COMPARATIVE EVALUATIONS
COSMOCHEMISTRY
DIAGRAMS
ECLIPSE
EMISSION SPECTRA
GENERAL CIRCULATION MODELS
INFRARED RADIATION
MARKOV PROCESS
MONTE CARLO METHOD
ORBITS
PLANETARY ATMOSPHERES
PLANETS
RADIANT HEAT TRANSFER
STARS
TELESCOPES
THERMAL EQUILIBRIUM