Day-side z′-band emission and eccentricity of wasp-12b

We report the detection of the eclipse of the very hot Jupiter WASP-12b via z′-band time-series photometry obtained with the 3.5 m Astrophysical Research Consortium telescope at Apache Point Observatory. We measure a decrease in flux of 0.082% 0.015% during the passage of the planet behind the star. That planetary flux is equally well reproduced by atmospheric models with and without extra absorbers, and blackbody models with f ≥ 0.585 ± 0.080. It is therefore necessary to measure the planet at other wavelengths to further constrain its atmospheric properties. The eclipse appears centered at phase φ = 0.5100^+0.0072 _-0.0061, consistent with an orbital eccentricity of |ecos ω| = 0.016^+0.011 _-0.009 (see note at the end of Section 4). If the orbit of the planet is indeed eccentric, the large radius of WASP-12b can be explained by tidal heating.