Francis T. O'Donovan et al. 2010 ApJ 710 1551 doi:10.1088/0004-637X/710/2/1551
Francis T. O'Donovan1,2,8, David Charbonneau3, Joseph Harrington4, N. Madhusudhan5, Sara Seager6, Drake Deming7 and Heather A. Knutson3
Show affiliationsWe present here the results of our observations of TrES-2 using the Infrared Array Camera on Spitzer. We monitored this transiting system during two secondary eclipses, when the planetary emission is blocked by the star. The resulting decrease in flux is 0.127% ± 0.021%, 0.230% ± 0.024%, 0.199% ± 0.054%, and 0.359% ± 0.060% at 3.6 μm, 4.5 μm, 5.8 μm, and 8.0 μm, respectively. We show that three of these flux contrasts are well fit by a blackbody spectrum with T eff = 1500 K, as well as by a more detailed model spectrum of a planetary atmosphere. The observed planet-to-star flux ratios in all four IRAC channels can be explained by models with and without a thermal inversion in the atmosphere of TrES-2, although with different atmospheric chemistry. Based on the assumption of thermochemical equilibrium, the chemical composition of the inversion model seems more plausible, making it a more favorable scenario. TrES-2 also falls in the category of highly irradiated planets which have been theoretically predicted to exhibit thermal inversions. However, more observations at infrared and visible wavelengths would be needed to confirm a thermal inversion in this system. Furthermore, we find that the times of the secondary eclipses are consistent with previously published times of transit and the expectation from a circular orbit. This implies that TrES-2 most likely has a circular orbit, and thus does not obtain additional thermal energy from tidal dissipation of a non-zero orbital eccentricity, a proposed explanation for the large radius of this planet.
eclipses; infrared: stars; planetary systems; stars: individual (GSC 03549-02811); techniques: photometric
Issue 2 (2010 February 20)
Received 2009 September 16, accepted for publication 2010 January 2
Published 2010 February 1
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