Featureless transmission spectra of 12 giant exoplanets observed by GTC/OSIRIS

TL;DR

This study used transit spectrophotometry to analyze 12 giant exoplanets' atmospheres, finding mostly featureless spectra which suggest cloudy or hazy atmospheres, with CoRoT-1b showing potential atmospheric features but requiring further investigation.

Contribution

First optical transmission spectra for 12 giant exoplanets were obtained and analyzed, revealing mostly featureless spectra and highlighting the need for more precise atmospheric characterization.

Findings

Most spectra were featureless, indicating cloudy or hazy atmospheres.

CoRoT-1b's spectrum shows potential atmospheric features but lacks definitive evidence.

Featureless spectra do not necessarily imply cloud-free atmospheres.

Abstract

Exoplanet atmospheres are the key to understanding the nature of exoplanets. To this end, transit spectrophotometry provides us opportunities to investigate the physical properties and chemical compositions of exoplanet atmospheres. We aim to detect potential atmospheric signatures in 12 gaseous giant exoplanets using transit spectrophotometry and we try to constrain their atmospheric properties. The targets of interest were observed using transit spectrophotometry with the GTC OSIRIS instrument. We estimated the transit parameters and obtained the optical transmission spectra of the target planets using a Bayesian framework. We analyzed the spectral features in the transmission spectra based on atmospheric retrievals. Most of the observed transmission spectra were found to be featureless, with only the spectrum of CoRoT-1b showing strong evidence for atmospheric features. However, in combination with the previously published near-infrared transmission spectrum, we found multiple interpretations for the atmosphere of CoRoT-1b due to the lack of decisive evidence for alkali metals or optical absorbers. Featureless spectra are not necessarily indicative of cloudy atmospheres if they poorly constrain the altitudes of cloud decks. Precise constraints on the models of hazes and clouds strongly depend on the significance of the observed spectral features. Further investigations on these exoplanets, especially CoRoT-1b, are required to confirm the properties of their atmospheres.