WASP-166

WASP-166, also named Filetdor, is an F-type main-sequence star away in the constellation Hydra. With an apparent magnitude of 9.4, it is too faint to be visible to the naked eye. It hosts one known exoplanet.

Nomenclature

The designation WASP-166 comes from the Wide Angle Search for Planets.
This was one of the 20 systems selected to be named in the third NameExoWorlds campaign, beginning in August 2022. The approved names, proposed by a team from Spain, were announced in June 2023. The star is named Filetdor and its planet is named Catalineta, after characters from a Mallorcan folktale about a golden sea serpent, Na Filet d'Or.

The planet WASP-166b, later named Catalineta, is a hot, low-density super-Neptune, discovered in 2018 using the transit method as part of the Wide Angle Search for Planets. It is a rare example of a planet within the Neptune desert; few Neptune-mass planets are found so close to their stars.
The orbit of WASP-166b is aligned with its host star's equator, differing from other similar hot Neptunes which have misaligned orbits. The aligned orbit suggests that it is unlikely to have undergone high-eccentricity migration.
While initial transmission spectroscopy observations of WASP-166b with the High Accuracy [Radial Velocity Planet Searcher|HARPS] spectrograph failed to detect any molecules in the planet's atmosphere, follow-up studies of the same dataset and of ESPRESSO data have detected sodium in the atmosphere. ESPRESSO has also been used to place constraints on the possible presence of water vapor and clouds.