Thermal emission spectra of the ultra-hot Jupiter WASP-33 b

TL;DR

This study characterizes the dayside atmosphere of ultra-hot Jupiter WASP-33 b using multi-band thermal emission spectra, revealing high metallicity, a thermal inversion, and molecular detections, informing its formation and evolution.

Contribution

It provides the first combined analysis of multiple observational datasets to determine atmospheric composition and structure of WASP-33 b, including tentative detection of TiO.

Findings

Eclipse depths of 1565 ppm (CO) and 914 ppm (CH4)$_{ m on}$

High metallicity ([Fe/H] ≈ 1.52) and C/O ratio (~0.78)

Detection of H$_{2}$O, H$^{-}$, CO, and tentative TiO

Abstract

Observations of exoplanetary atmospheres provide critical insights into their chemical composition, formation and evolution history. Ultra-hot Jupiters serve as excellent targets for atmospheric characterization; studies of these planets may yield key understanding of gas giant's formation and evolution history. We present a thermal emission study of WASP-33 b's dayside atmosphere, based on two secondary eclipse observations with CFHT/WIRCam in two specific narrow band filters, namely the CO and CH4$_{\rm on}$ filters, and archival data with HST/WFC3 and Spitzer. Stellar pulsations of the host star induce some quasi-periodic photometric variations, particularly in the CH4$_{\rm on}$ band, which are modelled and corrected in the high-precision differential light curves. An eclipse depth of $1565.2^{+228.6}_{-237.5}$ ppm and $914.3^{+56.1}_{-57.0}$ ppm is determined for the CO and CH4$_{\rm on}$ bands, respectively. Combined with HST/WFC3 and Spitzer data, our joint retrieval of WASP-33 b's dayside atmosphere reveals a high metallicity ([Fe/H] $= 1.52^{+0.35}_{-0.52}$), high C/O ratio (C/O $= 0.78^{+0.03}_{-0.04}$), and a thermal inversion layer, suggesting a formation history involving metal-rich gas accretion. We confirm the presence of the molecules H$_{2}$O, H$^{-}$ and CO, and report a tentative detection of TiO in the dayside atmosphere of WASP-33 b. Future higher precision observations with JWST may provide better understand constraints on the chemical abundances of oxygen and refractory element abundances to better WASP-33 b's formation and evolutionary pathway.