Detection of Thermal Emission from a Super-earth

We report on the detection of infrared light from the super-Earth 55Cnc e, based on four occultations obtained with Warm Spitzer at 4.5μm. Our data analysis consists of a two-part process. In a first step, we perform individual analyses of each dataset and compare several baseline models to optimally account for the systematics affecting each lightcurve. We apply independent photometric correction techniques, including polynomial detrending and pixel-mapping, that yield consistent results at the 1-σ level. In a second step, we perform a global MCMC analysis including all four datasets, that yields an occultation depth of 131± 28 ppm, translating to a brightness temperature of 2360± 300K in the IRAC-4.5μm channel. This occultation depth suggests a low Bond albedo coupled to an inefficient heat transport from the planetary dayside to the nightside, or else possibly that the 4.5μm observations probe atmospheric layers that are hotter than the maximum equilibrium temperature (i.e., a thermal inversion layer or a deep hot layer). The measured occultation phase and duration are consistent with a circular orbit and improves the 3-σ upper limit on 55Cnc e’s orbital eccentricity from 0.25 to 0.06. Subject headings: planetary systems stars: individual (55Cnc, HD 75732) techniques: photometric