Re-Evaluating WASP-12b: Strong Emission at 2.315 micron, Deeper Occultations, and an Isothermal Atmosphere

TL;DR

This study re-evaluates WASP-12b's atmosphere using new narrowband eclipse data, recent observations, and correction for stellar contamination, concluding its atmosphere is nearly isothermal and challenging previous abundance constraints.

Contribution

It provides new narrowband eclipse measurements, corrects for stellar contamination, and revises the atmospheric interpretation of WASP-12b to an almost isothermal state.

Findings

Planet's brightness temperature is approximately 3640 K.

Planet's emission spectrum is well-approximated by a blackbody.

Atmosphere is nearly isothermal, limiting abundance constraints.

Abstract

We revisit the atmospheric properties of the extremely hot Jupiter WASP-12b in light of several new developments. First, new narrowband (2.315 micron) secondary eclipse photometry that we present here, which exhibits a planet/star flux ratio of 0.45% +/- 0.06 %, corresponding to a brightness temperature of 3640 K +/- 230 K; second, recent Spitzer/IRAC and Hubble/WFC3 observations; and third, a recently observed star only 1" from WASP-12, which has diluted previous observations and which we further characterize here. We correct past WASP-12b eclipse measurements for the presence of this object, and we revisit the interpretation of WASP-12b's dilution-corrected emission spectrum. The resulting planetary emission spectrum is well-approximated by a blackbody, and consequently our primary conclusion is that the planet's infrared photosphere is nearly isothermal. Thus secondary eclipse spectroscopy is relatively ill-suited to constrain WASP-12b's atmospheric abundances, and transmission spectroscopy may be necessary to achieve this goal.