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Published January 1, 2009 | Accepted Version + Published
Journal Article Open

Multiwavelength Constraints on the Day-Night Circulation Patterns of HD 189733b


We present new Spitzer observations of the phase variation of the hot Jupiter HD 189733b in the MIPS 24 μm bandpass, spanning the same part of the planet's orbit as our previous observations in the IRAC 8 μm bandpass (Knutson et al. 2007). We find that the minimum hemisphere-averaged flux from the planet in this bandpass is 76% ± 3% of the maximum flux; this corresponds to minimum and maximum hemisphere-averaged brightness temperatures of 984 ± 48 K and 1220 ± 47 K, respectively. The planet reaches its maximum flux at an orbital phase of 0.396 ± 0.022, corresponding to a hot region shifted 20°-30° east of the substellar point. Because tidally locked hot Jupiters would have enormous day-night temperature differences in the absence of winds, the small amplitude of the observed phase variation indicates that the planet's atmosphere efficiently transports thermal energy from the day side to the night side at the 24 μm photosphere, leading to modest day-night temperature differences. The similarities between the 8 and 24 μm phase curves for HD 189733b lead us to conclude that the circulation on this planet behaves in a fundamentally similar fashion across the range of pressures sensed by these two wavelengths. One-dimensional radiative transfer models indicate that the 8 μm band should probe pressures 2-3 times greater than at 24 μm, although the uncertain methane abundance complicates the interpretation. If these two bandpasses do probe different pressures, it would indicate that the temperature varies only weakly between the two sensed depths, and hence that the atmosphere is not convective at these altitudes. We also present an analysis of the possible contribution of star spots to the time series at both 8 and 24 μm based on near-simultaneous ground-based observations and additional Spitzer observations. Accounting for the effects of these spots results in a slightly warmer night-side temperature for the planet in both bandpasses, but does not otherwise affect our conclusions.

Additional Information

© 2009 American Astronomical Society. Received 2008 February 13; accepted 2008 September 9; published 2008 December 1. We thank David Latham, Matthew Holman, Joshua Winn, Gilbert Esquerdo, José Fernandez, Gaspar Bakos, and César Fuentes for their assistance in obtaining observations of HD 189733 with the FLWO 1.2 m telescope, and for sharing time on their previously scheduled nights to obtain these observations. We thank Mark Marley for helpful discussions, and the referee for a thoughtful and detailed review. 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 contract to NASA. We also utilize observations made with KeplerCam, which was developed with partial support from the Kepler mission under Cooperative Agreement NCC2-1390. Support for this work was provided by NASA through an award issued by Jet Propulsion Laboratory/California Institute of Technology. H.A.K. was supported by a National Science Foundation Graduate Research Fellowship.

Attached Files

Published - 0004-637X_690_1_822.pdf

Accepted Version - 0802.1705.pdf


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