Atmospheric characterization of the ultra-hot Jupiter WASP-33b

Abstract

Ultra-hot Jupiters are highly irradiated gas giant exoplanets on close-in orbits around their host stars. The dayside atmospheres of these objects strongly emit thermal radiation due to their elevated temperatures, making them prime targets for characterization by emission spectroscopy. We analyzed high-resolution spectra from CARMENES, HARPS-N, and ESPaDOnS taken over eight observation nights to study the emission spectrum of WASP-33b and draw conclusions about its atmosphere. By applying the crosscorrelation technique, we detected the spectral signatures of Ti i, V i, and a tentative signal of Ti ii for the first time via emission spectroscopy. These detections are an important finding because of the fundamental role of Ti-and V-bearing species in the planetary energy balance. Moreover, we assessed and confirm the presence of OH, Fe i, and Si i from previous studies. The spectral lines are all detected in emission, which unambiguously proves the presence of an inverted temperature profile in the planetary atmosphere. By performing retrievals on the emission lines of all the detected species, we determined a relatively weak atmospheric thermal inversion extending from approximately 3400 K to 4000 K. We infer a supersolar metallicity close to 1.5 dex in the planetary atmosphere, and find that its emission signature undergoes significant line broadening with a Gaussian FWHM of about 4.5 km s −1 . Also, we find that the atmospheric temperature profile retrieved at orbital phases far from the secondary eclipse is about 300 K to 700 K cooler than that measured close to the secondary eclipse, which is consistent with different day-and nightside temperatures. Moreover, retrievals performed on the emission lines of the individual chemical species lead to consistent results, which gives additional confidence to our retrieval method. Increasing the number of species included in the retrieval and expanding the set of retrieved atmospheric parameters will further advance our understanding of exoplanet atmospheres.

Retrieval Survey of Metals in Six Ultrahot Jupiters: Trends in Chemistry, Rain-out, Ionization, and Atmospheric Dynamics

“…The ionic species also often probe the exosphere, which can make inferring abundances more challenging (e.g., Zhang et al 2022;Maguire et al 2023). In addition, we can also explore trends across the sample of planets in emission spectroscopy, which probe the hotter dayside and are more sensitive to the thermal profile of the atmosphere (e.g., Line et al 2021;Cont et al 2022;van Sluijs et al 2023;Brogi et al 2023).…”

“…On the other hand, the three planets with the lowest V abundances also possess the strongest RM and CLV, which may be interfering with the V signal in the observations. Cont et al (2022) suggest depleted V abundances for the UHJ WASP-33 b in emission compared with other species, showing that there may be some variation in inferred V abundances in UHJs.…”

“…Our findings are consistent with recent work from low-resolution retrievals, which showed at or near stellar abundances of alkali metals in hot Jupiters (e.g., ). On the other hand, recent high-resolution dayside observations of MAS-CARA-2 b and other ultrahot Jupiters have shown evidence for superstellar abundances (Cont et al 2022;Kasper et al 2023), indicating that there may be some variation in abundances of Fe in UHJs. Neutral Fe remains gaseous down to temperatures of ∼1350 K at 0.1 mbar (see Table 3), does not strongly ionize until high temperatures (see Figure 4), and is the dominant carrier of iron for these UHJs (Visscher et al 2010).…”

Keck Planet Imager and Characterizer Emission Spectroscopy of WASP-33b

“…Near-IR dayside observations have detected CO and OH in emission, but found only weak signs of H 2 O, indicative of high-temperature thermochemistry (Nugroho et al 2021;van Sluijs et al 2023;Yan et al 2022). Optical and NIR observations have detected a number of oxides and atomic species, including AlO (von Essen et al 2019), Si I (Cont et al 2022a), Fe I (Cont et al 2021;Herman et al 2022), Ti I, and V I (Cont et al 2022b), while transit observations of Balmer lines suggest an extended escaping hydrogen envelope driving mass loss at a rate of ∼10 12 g s −1 (Yan et al 2021). These observations have focused on dayside longitudes or the terminators, with phase-curve observations suggesting inefficient redistribution of heat to the nightside (Zhang et al 2018;Herman et al 2022).…”

A Two-limb Explanation for the Optical-to-infrared Transmission Spectrum of the Hot Jupiter HAT-P-32Ab

“…The 3D global circulation models have been used to investigate the compositions, distributions, and formation of clouds and how they shape the transmission and emission spectra (Parmentier et al 2016;Helling et al 2019Helling et al , 2021. Potential observational evidence for asymmetries resulting from atmospheric circulation has started to emerge through high-resolution Doppler spectroscopy (Ehrenreich et al 2020;van Sluijs et al 2022;Cont et al 2022).…”