Optical phase curve of the ultra-hot Jupiter WASP-121b

TL;DR

This study analyzes TESS optical data of the ultra-hot Jupiter WASP-121b, revealing its phase curve, hotspot location, heat transport inefficiency, and atmospheric composition, including temperature inversion and possible molecular contributors.

Contribution

First optical phase curve analysis of WASP-121b showing hotspot at substellar point and evidence for temperature inversion with specific atmospheric molecules.

Findings

Hotspot at substellar point indicating inefficient heat redistribution.

Eclipse depth confirms deviation from blackbody emission.

Atmospheric retrieval suggests temperature inversion with VO, TiO, FeH.

Abstract

We present the analysis of TESS optical photometry of WASP-121b, which reveal the phase curve of this transiting ultra-hot Jupiter. Its hotspot is located at the substellar point, showing inefficient heat transport from the dayside (2870 K) to the nightside ($<$ 2200 K) at the altitudes probed by TESS. The TESS eclipse depth, measured at the shortest wavelength to date for WASP-121b, confirms the strong deviation from blackbody planetary emission. Our atmospheric retrieval on the complete emission spectrum supports the presence of a temperature inversion, which can be explained by the presence of VO and possibly TiO and FeH. The strong planetary emission at short wavelengths could arise from an H$^{-}$ continuum.