NEAR-INFRARED THERMAL EMISSION FROM THE HOT JUPITER TrES-2b: GROUND-BASED DETECTION OF THE SECONDARY ECLIPSE

We present near-infrared Ks-band photometry bracketing the secondary eclipse of the hot Jupiter TrES-2b using the Wide-field Infrared Camera on the Canada-France-Hawaii Telescope. We detect its thermal emission with an eclipse depth of 0.062(-0.011)(+0.013) % (5 sigma). Our best-fit secondary eclipse is consistent with a circular orbit (a 3 sigma upper limit on the eccentricity, e, and argument or periastron, omega, of vertical bar e cos omega vertical bar < 0.0090), in agreement with mid-infrared detections of the secondary eclipse of this planet. A secondary eclipse of this depth corresponds to a dayside Ks-band brightness temperature of T-B = 1636(-88)(+79) K. Our thermal emission measurement, when combined with the thermal emission measurements using Spitzer/IRAC from O'Donovan and collaborators, suggests that this planet exhibits relatively efficient dayside to nightside redistribution of heat and a near isothermal dayside atmospheric temperature structure, whose spectrum is well approximated by a blackbody. It is unclear if the atmosphere of TrES-2b requires a temperature inversion; if it does it is likely due to chemical species other than TiO/VO as the atmosphere of TrES-2b is too cool to allow TiO/VO to remain in gaseous form. Our secondary eclipse has the smallest depth of any detected from the ground, at around 2 mu m, to date.