Inferring heat recirculation and albedo for exoplanetary atmospheres: Comparing optical phase curves and secondary eclipse data

Abstract

Basic atmospheric properties such as albedo and heat redistribution between day and nightside have been inferred for a number of planets using observations of secondary eclipses and thermal phase curves. Optical phase curves have not yet been used to constrain these atmospheric properties consistently. We re-model previously published phase curves of CoRoT-1b, TrES-2b and HAT-P-7b and infer albedos and recirculation efficiencies. These are then compared to previous estimates based on secondary eclipse data. We use a physically consistent model to construct optical phase curves. This model takes Lambertian reflection, thermal emission, ellipsoidal variations and Doppler boosting into account. CoRoT-1b shows a non-negligible scattering albedo (0.11<AS<0.3 at 95% confidence) as well as small day-night temperature contrasts, indicative of moderate to high re-distribution of energy between dayside and nightside. These values are contrary to previous secondary eclipse and phase curve analyses. In the case of HAT-P-7b, model results suggest relatively high scattering albedo (AS=0.3). This confirms previous phase curve analysis, however, it is in slight contradiction to values inferred from secondary eclipse data. For TrES-2b, both approaches yield very similar estimates of albedo and heat recirculation. Discrepancies between recirculation and albedo values as inferred from secondary eclipse and optical phase curve analyses might be interpreted as a hint that optical and IR observations probe different atmospheric layers, and hence temperatures.