Near-infrared Thermal Emission from WASP-12b: detections of the secondary eclipse in Ks, H & J

TL;DR

This study detects thermal emission from exoplanet WASP-12b in three near-infrared bands, constrains its orbital and atmospheric properties, and explores potential signs of tidal stripping, advancing understanding of highly irradiated hot Jupiters.

Contribution

First near-infrared detection of thermal emission from WASP-12b across Ks, H, and J bands, providing new insights into its atmosphere and orbital characteristics.

Findings

Secondary eclipse depths measured in Ks, H, and J bands.

Orbital eccentricity likely zero, no evidence of precession.

Hints of a temperature inversion in the atmosphere.

Abstract

We present Ks, H & J-band photometry of the very highly irradiated hot Jupiter WASP-12b using the Wide-field Infrared Camera on the Canada-France-Hawaii telescope. Our photometry brackets the secondary eclipse of WASP-12b in the Ks and H-bands, and in J-band starts in mid-eclipse and continues until well after the end of the eclipse. We detect its thermal emission in all three near-infrared bands. Our secondary eclipse depths are 0.309 +/- 0.013% in Ks-band (24-sigma), 0.176 +/- 0.020% in H-band (9-sigma) and 0.131 +/- 0.028% in J-band (4-sigma). All three secondary eclipses are best-fit with a consistent phase that is compatible with a circular orbit. By combining our secondary eclipse times with others published in the literature, as well as the radial velocity and transit timing data for this system, we show that there is no evidence that WASP-12b is precessing at a detectable rate, and show that its orbital eccentricity is likely zero. Our thermal emission measurements also allow us to constrain the characteristics of the planet's atmosphere; our Ks-band eclipse depth argues in favour of inefficient day to nightside redistribution of heat and a low Bond albedo for this very highly irradiated hot Jupiter. The J and H-band brightness temperatures are slightly cooler than the Ks-band brightness temperature, and thus hint at the possibility of a modest temperature inversion deep in the atmosphere of WASP-12b; the high pressure, deep atmospheric layers probed by our J and H-band observations are likely more homogenized than the higher altitude layer. Lastly, our best-fit Ks-band eclipse has a marginally longer duration than would otherwise be expected; this may be tentative evidence for material being tidally stripped from the planet - as was predicted for this system by Li & collaborators, and for which observational confirmation was recently arguably provided by Fossati & collaborators.