Probing the atmosphere of WASP-69 b with low- and high-resolution transmission spectroscopy

Abstract

Consideration of both low- and high-resolution transmission spectroscopy is key for obtaining a comprehensive picture of exoplanet atmospheres. In studies of transmission spectra, the continuum information is well established with low-resolution spectra, while the shapes of individual lines are best constrained with high-resolution observations. In this work, we aim to merge high- with low-resolution transmission spectroscopy. We present the analysis of three primary transits of WASP-69b in the VIS channel of the CARMENES instrument and perform a combined low- and high-resolution analysis using additional data from HARPS-N, OSIRIS/GTC, and WFC3/HST already available in the literature. During the first CARMENES observing night, we detected the planet Na D${}_2$ and D${}_1$ lines at $\sim 7\sigma$ and $\sim 3\sigma$ significance levels, respectively. We measured a D${}_2$/D${}_1$ intensity ratio of 2.5$\pm$0.7, which is in agreement with previous HARPS-N observations. Our modelling of WFC3 and OSIRIS data suggests strong Rayleigh scattering, solar to super-solar water abundance, and a highly muted Na feature in the atmosphere of this planet, in agreement with previous investigations of this target. We use the continuum information retrieved from the low-resolution spectroscopy as a prior to break the degeneracy between the Na abundance, reference pressure, and thermosphere temperature for the high-resolution spectroscopic analysis. We fit the Na D${}_1$ and D${}_2$ lines individually and find that the posterior distributions of the model parameters agree with each other within 1$\sigma$. Our results suggest that local thermodynamic equilibrium processes can explain the observed D${}_2$/D${}_1$ ratio because the presence of haze opacity mutes the absorption features.

20 pages, 18 figures, accepted for publication in A&A

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