First Detection of Hydroxyl Radical Emission from an Exoplanet Atmosphere: High-dispersion Characterization of WASP-33b Using Subaru/IRD

Abstract

We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the dayside of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2 m Subaru telescope. The telluric and stellar lines are removed using a detrending algorithm, SysRem. The residuals are then cross-correlated with OH and H2O planetary spectrum templates produced using several different line lists. We check and confirm the accuracy of OH line lists by cross-correlating with the spectrum of GJ 436. As a result, we detect the emission signature of OH at K p of km s−1 and v sys of −0.3 km s−1 with a signal-to-noise ratio (S/N) of 5.4 and a significance of 5.5σ. Additionally, we marginally detect H2O emission in the H-band with an S/N of 4.0 and a significance of 5.2σ using the POKAZATEL line list. However, no significant signal is detected using the HITEMP 2010, which might be due to differences in line positions and strengths, as well as the incompleteness of the line lists. Nonetheless, this marginal detection is consistent with the prediction that H2O is mostly thermally dissociated in the upper atmosphere of the ultra-hot Jupiters. Therefore, along with CO, OH is expected to be one of the most abundant O-bearing molecules in the dayside atmosphere of ultra-hot Jupiters and should be considered when studying their atmospheres.

Carbon monoxide emission lines reveal an inverted atmosphere in the ultra hot Jupiter WASP-33 b and indicate an eastward hot spot

“…Despite the elusive results for TiO, several new detections suggest WASP-33 b must have a thermally inverted atmosphere. Recently, emission signatures of FeI (Nugroho et al 2020b;Cont et al 2021a), neutral Si (Cont et al 2021b) and OH (Nugroho et al 2021) have been detected. Nugroho et al (2021) also marginally detect H 2 O, consistent with the theoretical predictions that H 2 O molecules dissociate into OH and H − at the temperature regime of UHJs.…”

Modelling high-resolution transmission spectra of the ultra-hot jupiter wasp-76b with 3D Monte-Carlo radiative transfer

“…In spite of some numerical discrepancies, the same trends could be recovered, suggesting that our analysis is at least qualitatively robust. Furthermore, all CCF maps shown in this work (see Sections 5 and 6) are obtained by adding the maps of both wavelength windows together -analogous to combining the signals from different spectral orders in real observations (e.g., Nugroho et al 2021).…”

Relative abundance constraints from high-resolution optical transmission spectroscopy of WASP-121b, and a fast model-filtering technique for accelerating retrievals

“…It can be seen as a generalisation of PCA that accounts for uncertainties in the data array, and has therefore become the method of choice for model-independent filtering of high-resolution data (e.g. Birkby et al 2017;Esteves et al 2017;Nugroho et al 2021); however, more recent studies performing retrievals have reverted to basismodel fitting or PCA which can be applied more quickly within each likelihood calculation (e.g. Brogi & Line 2019;Pelletier et al 2021;Line et al 2021), whereas S R is an iterative process and is much too slow.…”

“…This approach to detecting species in exoplanet atmospheres has flourished in recent years, with detections of multiple molecular, atomic and ionised species in a wide range of planetary atmospheres (e.g. Hoeijmakers et al 2018;Ehrenreich et al 2020;Pelletier et al 2021;Nugroho et al 2021;Giacobbe et al 2021;Merritt et al 2021).…”