Detection of A Temperature Inversion in the Broadband Infrared Emission Spectrum of TrES-4
We estimate the strength of the bandpass-integrated thermal emission from the extrasolar planet TrES-4 at 3.6, 4.5, 5.8, and 8.0 μ using the Infrared Array Camera on the Spitzer Space Telescope. We find relative eclipse depths of 0.137% ± 0.011%, 0.148% ± 0.016%, 0.261% ± 0.059%, and 0.318% ± 0.044% in these four bandpasses, respectively. We also place a 2σ upper limit of 0.37% on the depth of the secondary eclipse in the 16 μ IRS peak-up array. These eclipse depths reveal that TrES-4 has an emission spectrum similar to that of HD 209458b, which requires the presence of water emission bands created by a thermal inversion layer high in the atmosphere in order to explain the observed features. TrES-4 receives more radiation from its star than HD 209458b and has a correspondingly higher effective temperature, therefore the presence of a temperature inversion in this planet's atmosphere lends support to the idea that inversions might be correlated with the irradiance received by the planet. We find no evidence for any offset in the timing of the secondary eclipse, and place a 3σ upper limit of |ecos(ω)| < 0.0058, where e is the planet's orbital eccentricity and ω is the argument of pericenter. From this we conclude that tidal heating from ongoing orbital circularization is unlikely to be the explanation for TrES-4's inflated radius.
Additional Information© 2009 American Astronomical Society. Received 2008 August 1; accepted 2008 September 30; published 2009 January 19. 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. Support for this work was provided by NASA through an award issued by JPL/Caltech. H.A.K. was supported by a National Science Foundation Graduate Research Fellowship. A.B. acknowledges the support of NASA through grant NNX07AG80G and JPL/Spitzer Agreement no. 1328902 and through the NASA Astrobiology Institute under Cooperative Agreement no. CAN-02-OSS-02 issued through the Office of Space Science. A.B. would also like to acknowledge Laurent Ibgui for checking the model results. F.T.O'D. was supported by an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA.
Published - 0004-637X_691_1_866.pdf
Accepted Version - 0810.0021.pdf