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Abstract:

Determining the composition of an exoplanet atmosphere relies on the presence of detectable spectral features. The strongest spectral features, including dimethyl sulphide (DMS), look approximately Gaussian. Here, I perform a suite of Gaussian feature analyses to find any statistically significant spectral features in the recently published MIRI/LRS spectrum of K2-18b. In N. Madhusudhan et al., they claim a 3.4σ detection of spectral features compared to a flat line. In 5 out of 6 tests, I find the data preferred a flat line over a Gaussian model, with a χν2 of 1.06. When centering the Gaussian where the absorptions for DMS and DMDS peak, I find ln(B) = 1.21 in favour of the Gaussian model, with a χν2 of 0.99. With only ∼2σ in favour of Gaussian features, I conclude no strong statistical evidence for spectral features.

Abstract:

Secondary eclipse observations of exoplanets at near-infrared wavelengths enable the detection of thermal emission and reflected stellar light, providing insights into the thermal structure and aerosol composition of their atmospheres. These properties are intertwined as aerosols influence the energy budget of the planet. WASP-80 b is a warm gas giant with an equilibrium temperature of 825 K orbiting a bright late-K/early-M dwarf, and for which the presence of aerosols in its atmosphere has been suggested from previous Hubble Space Telescope and Spitzer observations. We present an eclipse spectrum of WASP-80 b obtained with JWST NIRISS/SOSS, spanning 0.68–2.83 μm, which includes the first eclipse measurements below 1.1 μm for this exoplanet, extending our ability to probe light reflected by its atmosphere. When a reflected light geometric albedo is included in the atmospheric retrieval, our eclipse spectrum is best explained by a reflected light contribution of ∼30 ppm at short wavelengths, although further observations are needed to statistically confirm this preference. We measure a dayside brightness temperature of TB=811−70+69 K and constrain the reflected light geometric albedo across the SOSS wavelength range to Ag=0.204−0.056+0.051 , allowing us to estimate a 1σ range for the Bond albedo of 0.148 ≲ AB ≲ 0.383. By comparing our spectrum with aerosol models, we find that manganese sulfide and silicate clouds are disfavored, while cloud species with weak-to-moderate near-infrared reflectance, along with soots or low formation-rate tholin hazes, are consistent with our eclipse spectrum.