The GTC exoplanet transit spectroscopy survey IX. Detection of Haze, Na, K, and Li in the super-Neptune WASP-127b

TL;DR

This study reports the detection of pressure-broadened alkali metal lines and haze in the atmosphere of exoplanet WASP-127b using high-quality optical transmission spectra, providing insights into its atmospheric composition and cloud coverage.

Contribution

First detection of pressure-broadened Na, K, and Li lines in WASP-127b's atmosphere using combined GTC and NOT spectra, with atmospheric retrieval modeling revealing super-solar abundances and haze coverage.

Findings

Detected pressure-broadened Na, K, and Li lines at high significance levels.

Retrieved super-solar abundances of K and Li, with limited Na detection.

Constrained haze coverage to approximately 52%.

Abstract

Exoplanets with relatively clear atmospheres are prime targets for detailed studies of chemical compositions and abundances in their atmospheres. Alkali metals have long been suggested to exhibit broad wings due to pressure broadening, but most of the alkali detections only show very narrow absorption cores, probably because of the presence of clouds. We report the strong detection of the pressure-broadened spectral profiles of Na, K, and Li absorption in the atmosphere of the super-Neptune WASP-127b, at 4.1$\sigma$, 5.0$\sigma$, and 3.4$\sigma$, respectively. We performed a spectral retrieval modeling on the high-quality optical transmission spectrum newly acquired with the 10.4 m Gran Telescopio Canarias (GTC), in combination with the re-analyzed optical transmission spectrum obtained with the 2.5 m Nordic Optical Telescope (NOT). By assuming a patchy cloudy model, we retrieved the abundances of Na, K, and Li, which are super-solar at 3.7$\sigma$ for K and 5.1$\sigma$ for Li (and only 1.8$\sigma$ for Na). We constrained the presence of haze coverage to be around 52%. We also found a hint of water absorption, but cannot constrain it with the global retrieval owing to larger uncertainties in the probed wavelengths. WASP-127b will be extremely valuable for atmospheric characterization in the era of James Webb Space Telescope.