On the heat redistribution of the hot transiting exoplanet WASP-18b

TL;DR

This paper models heat redistribution in the atmosphere of the hot Jupiter WASP-18b, finding that inefficient heat transfer explains observed fluxes, with implications for atmospheric dynamics and observational signatures.

Contribution

It introduces a time-dependent radiative transfer model incorporating simplified energy redistribution, comparing rotation scenarios to explain observational data of WASP-18b.

Findings

Heat redistribution in WASP-18b is highly inefficient.

No atmospheric rotation best explains observed fluxes.

Light curves differ significantly between rotation scenarios.

Abstract

The energy deposition and redistribution in hot Jupiter atmospheres is not well understood currently, but is a major factor for their evolution and survival. We present a time dependent radiative transfer model for the atmosphere of WASP-18b which is a massive (10 MJup) hot Jupiter (Teq ~ 2400 K) exoplanet orbiting an F6V star with an orbital period of only 0.94 days. Our model includes a simplified parametrisation of the day-to-night energy redistribution by a modulation of the stellar heating mimicking a solid body rotation of the atmosphere. We present the cases with either no rotation at all with respect to the synchronously rotating reference frame or a fast differential rotation. The results of the model are compared to previous observations of secondary eclipses of Nymeyer et al. (2011) with the Spitzer Space Telescope. Their observed planetary flux suggests that the efficiency of heat distribution from the day-side to the night-side of the planet is extremely inefficient. Our results are consistent with the fact that such large day-side fluxes can be obtained only if there is no rotation of the atmosphere. Additionally, we infer light curves of the planet for a full orbit in the two Warm Spitzer bandpassses for the two cases of rotation and discuss the observational differences.