Žák, J.; Kabáth, P.; Boffin, H. M. J.; Ivanov, V. D.; and Skarka, M.; 2019, AJ, 158, 3.:

    High-resolution transmission spectroscopy of four hot inflated gas giant exoplanets

    The technique of transmission spectroscopy allows us to constrain the chemical composition of the atmospheres of transiting exoplanets. In this study our group in collaboration with ESO investigated four hot inflated gas giant exoplanets to study their atmospheres. Using spectroscopic data from the HARPS instrument we were able to detect sodium presence in the atmospheres of WASP-76b and WASP-127b. No detections were reported for exoplanets WASP-166b and KELT-11b hinting at the presence of thick high clouds.

Spectral region around the sodium doublet for one of our four targets, removing the stellar signature.
Sodium is clearly detected. The blue dashed lines indicate the position of the Na D2 and D1 lines.