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Statistical Characterization of Hot Jupiter Atmospheres using Spitzer's Secondary Eclipses

Published version
Peer-reviewed

Type

Article

Change log

Authors

Garhart, Emily 
Deming, Drake 
Mandell, Avi 
Knutson, Heather A 
Wallack, Nicole 

Abstract

We report 78 secondary eclipse depths for a sample of 36 transiting hot Jupiters observed at 3.6- and 4.5 microns using the Spitzer Space Telescope. Our eclipse results for 27 of these planets are new, and include highly irradiated worlds such as KELT-7b, WASP-87b, WASP-76b, and WASP-64b, and important targets for JWST such as WASP-62b. We find that WASP-62b has a slightly eccentric orbit e cos(omega) = 0.00614+/- 0.00064, and we confirm the eccentricity of HAT-P-13b and WASP-14b. The remainder are individually consistent with circular orbits, but we find statistical evidence for eccentricity increasing with orbital period in our range from 1 to 5 days. Our day-side brightness temperatures for the planets yield information on albedo and heat redistribution, following Cowan and Agol (2011). Planets having maximum day side temperatures exceeding ~ 2200K are consistent with zero albedo and distribution of stellar irradiance uniformly over the day-side hemisphere. Our most intriguing result is that we detect a systematic difference between the emergent spectra of these hot Jupiters as compared to blackbodies. The ratio of observed brightness temperatures, Tb(4.5)/Tb(3.6), increases with equilibrium temperature by 100 +/- 24 parts-per-million per Kelvin, over the entire temperature range in our sample (800K to 2500K). No existing model predicts this trend over such a large range of temperature. We suggest that this may be due to a structural difference in the atmospheric temperature profile between the real planetary atmospheres as compared to models.

Description

Keywords

Exoplanet astronomy, Exoplanet atmospheric composition, Exoplanet atmospheres

Journal Title

The Astronomical Journal

Conference Name

Journal ISSN

0004-6256
1538-3881

Volume Title

Publisher

Institute of Physics Publishing

Rights

All rights reserved
Sponsorship
Science and Technology Facilities Council (ST/N000927/1)