We have used Hubble/WFC3 and the G141 grism to measure the secondary eclipse of the transiting very hot Jupiter CoRoT-2b in the 1.1-1.7 \mu m spectral region .
We find an eclipse depth averaged over this band equal to 395 ^ { +69 } _ { -45 } parts per million , equivalent to a blackbody temperature of 1788 \pm 18 K. We study and characterize several WFC3 instrumental effects , especially the “ hook ” phenomenon described by Deming et al .
( 13 ) .
We use data from several transiting exoplanet systems to find a quantitative relation between the amplitude of the hook and the exposure level of a given pixel .
Although the uncertainties in this relation are too large to allow us to develop an empirical correction for our data , our study provides a useful guide for optimizing exposure levels in future WFC3 observations .
We derive the planet ’ s spectrum using a differential method .
The planet-to-star contrast increases to longer wavelength within the WFC3 bandpass , but without water absorption or emission to a 3 \sigma limit of 85 ppm .
The slope of the WFC3 spectrum is significantly less than the slope of the best-fit blackbody .
We compare all existing eclipse data for this planet to a blackbody spectrum , and to spectra from both solar abundance and carbon-rich ( C/O=1 ) models .
A blackbody spectrum is an acceptable fit to the full dataset .
Extra continuous opacity due to clouds or haze , and flattened temperature profiles , are strong candidates to produce quasi-blackbody spectra , and to account for the amplitude of the optical eclipses .
Our results show ambiguous evidence for a temperature inversion in this planet .