WASP-63

WASP-63 or Kosjenka, also known as CD-38 2551, is a single star with an exoplanetary companion in the southern constellation of Columba. It is too faint to be visible with the naked eye, having an apparent visual magnitude of 11.1. The distance to this system is approximately 942 ly based on parallax measurements, but it is drifting closer with a radial velocity of −24 km/s.

Nomenclature
The designation WASP-63 indicates that this was the 63rd star found to have a planet by the Wide Angle Search for Planets.

In August 2022, this planetary system was included among 20 systems to be named by the third NameExoWorlds project. The approved names, proposed by a team from Croatia, were announced in June 2023. WASP-63 is named Kosjenka and its planet is named Regoč, after characters from Croatian Tales of Long Ago by Ivana Brlić-Mažuranić.

Stellar properties
This is a G-type star with a stellar classification of G8; the luminosity class is currently unknown. The star is much older than the Sun at approximately 8.3$$ billion years. WASP-63 is slightly enriched in heavy elements, having 120% of the solar abundance of iron. The stellar radius is enlarged for a G8 star, and models suggest it has evolved into a subgiant star. It has 1.1 times the mass of the Sun and is spinning with a projected rotational velocity of 3 km/s.

Planetary system
In 2012 a transiting gas giant planet WASP-63b was detected on a tight, circular orbit. Its equilibrium temperature is $$, and measured dayside temperature is $$. The planet is similar to Saturn in mass but is highly inflated due to proximity to the parent star. The planetary atmosphere contains water and likely has a high cloud deck of indeterminate composition.