Spectroscopic Evidence for a Temperature Inversion in the Dayside Atmosphere of the Hot Jupiter WASP-33b

TL;DR

This study uses HST/WFC3 observations of WASP-33b to reveal a temperature inversion in its atmosphere, likely caused by TiO, marking the first such detection in a hot Jupiter orbiting a delta-Scuti star.

Contribution

It provides the first spectroscopic evidence of a temperature inversion in a hot Jupiter's atmosphere due to TiO, using space-based observations and atmospheric modeling.

Findings

Evidence of a temperature inversion in WASP-33b's atmosphere.

Detection of excess flux at short wavelengths attributed to TiO emission.

Atmospheric models favor oxygen-rich composition with increasing temperature at high altitudes.

Abstract

We present observations of two occultations of the extrasolar planet WASP-33b using the Wide Field Camera 3 (WFC3) on the HST, which allow us to constrain the temperature structure and composition of its dayside atmosphere. WASP-33b is the most highly irradiated hot Jupiter discovered to date, and the only exoplanet known to orbit a delta-Scuti star. We observed in spatial scan mode to decrease instrument systematic effects in the data, and removed fluctuations in the data due to stellar pulsations. The RMS for our final, binned spectrum is approximately 1.05 times the photon noise. We compare our final spectrum, along with previously published photometric data, to atmospheric models of WASP-33b spanning a wide range in temperature profiles and chemical compositions. We find that the data require models with an oxygen-rich chemical composition and a temperature profile that increases at high altitude. We also find that our spectrum displays an excess in the measured flux towards short wavelengths that is best explained as emission from TiO. If confirmed by additional measurements at shorter wavelengths, this planet would become the first hot Jupiter with a temperature inversion that can be definitively attributed to the presence of TiO in its dayside atmosphere.