Day-side z'-band emission and eccentricity of Wasp-12b

TL;DR

This study detects the day-side z'-band emission of Wasp-12b, indicating a possible eccentric orbit and suggesting tidal heating as a reason for its large radius, with implications for atmospheric characterization.

Contribution

First measurement of Wasp-12b's z'-band eclipse, providing constraints on its atmospheric properties and orbital eccentricity, using ground-based photometry.

Findings

Detected 0.082% flux decrease during eclipse

Orbital phase consistent with slight eccentricity

Eccentricity could explain large planetary radius

Abstract

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-meter ARC 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 = 0.5100 (+0.0072,-0.0061), consistent with an orbital eccentricity of |e cos w| = 0.016 (+0.011,-0.009) (see note at 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.