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Phase Curves of WASP-33b and HD 149026b and a New Correlation between Phase Curve Offset and Irradiation Temperature

Zhang, Michael and Knutson, Heather A. and Kataria, Tiffany and Schwartz, Joel C. and Cowan, Nicolas B. and Showman, Adam P. and Burrows, Adam and Fortney, Jonathan J. and Todorov, Kamen and Desert, Jean-Michel and Agol, Eric and Deming, Drake (2018) Phase Curves of WASP-33b and HD 149026b and a New Correlation between Phase Curve Offset and Irradiation Temperature. Astronomical Journal, 155 (2). Art. No. 83. ISSN 1538-3881.

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We present new 3.6 and 4.5 μm Spitzer phase curves for the highly irradiated hot Jupiter WASP-33b and the unusually dense Saturn-mass planet HD 149026b. As part of this analysis, we develop a new variant of pixel-level decorrelation that is effective at removing intrapixel sensitivity variations for long observations (>10 hr) where the position of the star can vary by a significant fraction of a pixel. Using this algorithm, we measure eclipse depths, phase amplitudes, and phase offsets for both planets at 3.6 and 4.5 μm. We use a simple toy model to show that WASP-33b's phase offset, albedo, and heat recirculation efficiency are largely similar to those of other hot Jupiters despite its very high irradiation. On the other hand, our fits for HD 149026b prefer a very high albedo. We also compare our results to predictions from general circulation models, and we find that while neither planet matches the models well, the discrepancies for HD 149026b are especially large. We speculate that this may be related to its high bulk metallicity, which could lead to enhanced atmospheric opacities and the formation of reflective cloud layers in localized regions of the atmosphere. We then place these two planets in a broader context by exploring relationships between the temperatures, albedos, heat transport efficiencies, and phase offsets of all planets with published thermal phase curves. We find a striking relationship between phase offset and irradiation temperature: the former drops with increasing temperature until around 3400 K and rises thereafter. Although some aspects of this trend are mirrored in the circulation models, there are notable differences that provide important clues for future modeling efforts.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Zhang, Michael0000-0002-0659-1783
Knutson, Heather A.0000-0002-0822-3095
Kataria, Tiffany0000-0003-3759-9080
Schwartz, Joel C.0000-0001-5232-9957
Cowan, Nicolas B.0000-0001-6129-5699
Burrows, Adam0000-0002-3099-5024
Fortney, Jonathan J.0000-0002-9843-4354
Todorov, Kamen0000-0002-9276-8118
Desert, Jean-Michel0000-0002-0875-8401
Agol, Eric0000-0002-0802-9145
Deming, Drake0000-0001-5727-4094
Additional Information:© 2018 American Astronomical Society. Received 2017 October 19. Accepted 2017 December 26. Published 2018 January 24. 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. acknowledges support from the Sloan Foundation.
Group:Astronomy Department
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords:astrochemistry; magnetohydrodynamics (MHD) ; methods: data analysis; planetary systems; planets and satellites: atmospheres; planets and satellites: individual (HD 149026b, WASP-33b)
Issue or Number:2
Record Number:CaltechAUTHORS:20180131-134041261
Persistent URL:
Official Citation:Michael Zhang et al 2018 AJ 155 83
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84606
Deposited By: Ruth Sustaita
Deposited On:31 Jan 2018 22:08
Last Modified:20 Apr 2020 08:47

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