No Detection of Sodium in the Atmosphere of the Warm Neptune HD 106315c

Abstract

We analyzed archival data of the warm Neptune HD 106315c, an exoplanet with an extended atmosphere orbiting an F-type star with a 21 days period. We used data from the HARPS instrument covering three transits and employed the high-resolution transmission spectroscopy technique. Our analysis yielded a non-detection of sodium with an upper limit of 0.24% on the depth of the planetary feature. This can hint at the presence of Rayleigh scattering in the atmosphere and/or clouds in the upper atmosphere. The HD 106315 system with its two Neptune-sized planets remains an intriguing target for comparative planetology in the starting era of JWST and the upcoming Ariel mission.