TrES-2 b IR detection

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TrES-2 b IR detection

Post by Sirius_Alpha on 16th September 2009, 8:35 pm

Detection of Planetary Emission from the Exoplanet TrES-2 using Spitzer /IRAC

Abstract wrote:With the recent torrent of discoveries of new transiting planets, there have been ample candidates for observations using the Spitzer Space Telescope. We 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, 4.5, 5.8, and 8.0 microns, respectively. We show that three of these flux contrasts are well fit by a black body spectrum with Teff = 1500 K, as well as by a more detailed model spectrum of a planetary atmosphere. However, the planet-to-star flux ratio at 4.5 microns exceeds the expectation from the blackbody emission, which argues for a temperature inversion in the atmosphere of TrES-2. The presence or absence of such an inversion in a planetary atmosphere has been predicted to be correlated with the amount of incident flux received by the planet, with hotter planets like TrES-2 being more likely to exhibit this inversion. Our observation of emission at 4.5 microns that is indicative of an inversion supports the proposed importance of TiO and VO opacities in atmospheric models of highly irradiated gas giants. 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.

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