Bright optical dayside emission from extrasolar planet CoRoT-2b

Abstract

We present our analysis of the red-channel CoRoT data of CoRoT-2b. A deep secondary eclipse is detected at a level of 1.02+-0.20 x10-4, which suggests that all of the planet-signal detected previously in white light by Alonso et al. (2009) originates from the red channel. CoRoT-2b is the coolest exoplanet that has been detected in the optical so far. In contrast to the other planets, its measured brightness temperature of 2170+-55 K is significantly higher than its maximum hemisphere-averaged effective day-side temperature. However, it is not expected that a hot Jupiter radiates as a black body, and its thermal spectrum can deviate significantly from a Planck curve. We present models of the planet/star flux ratio as function of wavelength, which are calculated for a T/P profile in radiative and hydrostatic equilibrium, using a self-consistent atmosphere code. These are compared with the CoRoT detection, and with measurements at 4.5 and 8 um from the Spitzer Space Telescope from Gillon et al. (2009). We estimate that reflected light contributes only at a 10-20% level to the total optical eclipse depth. The models allow for an 'extra absorber' to be inserted at high altitude in the planet's atmosphere. This produces a thermal inversion layer, recently invoked to explain the photometric reversals and flux enhancements seen in some planets in the infrared. In the 0.5-1.5 um wavelength range, the model-spectra of planets with an extra absorber at high altitude, are relatively suppressed in flux compared to those without such absorber. We therefore argue that, in contrast to the other exoplanets detected in the optical so far, CoRoT-2b may not exhibit a significant thermal inversion in its atmosphere, causing its optical brightness temperature to be boosted above its maximum effective day-side temperature.

9 pages latex: Astronomy and Astrophysics, accepted

References in corpus (9)

• Theoretical Spectral Models of the Planet HD 209458b with a Thermal Inversion and Water Emission Bands
• The Very Low Albedo of an Extrasolar Planet: MOST Spacebased Photometry of HD 209458
• The changing phases of extrasolar planet CoRoT-1b
• The thermal emission of the young and massive planet CoRoT-2b at 4.5 and 8 microns
• Optical Albedo Theory of Strongly-Irradiated Giant Planets: The Case of HD 209458b
• Ground-based secondary eclipse detection of the very-hot Jupiter OGLE-TR-56b
• The secondary eclipse of the transiting exoplanet CoRoT-2b
• Reflected light from 3D exoplanetary atmospheres and simulation of HD 209458b
• Magnetic activity in the photosphere of CoRoT-Exo-2a. Active longitudes and short-term spot cycle in a young Sun-like star

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