DS Tucanae


DS Tucanae is a binary star system in the constellation of Tucana. It has an apparent visual magnitude of 8.5, and is a RS Canum Venaticorum variable. The system is notable for being young as a member of the 45 Myr old Tucana-Horologium moving group and for the primary star hosting the confirmed exoplanet DS Tucanae Ab, discovered by TESS.

Stellar System

DS Tucanae is a visual binary. The binary consists of a G6V primary and a K3V secondary separated by 5". Based on radial velocity measurements it was suggested that the secondary itself is a binary, but later studies could not find evidence for this claim.

Physical properties

High levels of magnetic activity, a strong 6708Å lithium line, and the position on the color-magnitude diagram, slightly above the main sequence, strongly support a young age of the system.

Planetary System

DS Tuc Ab is one of the few transiting planets with an age smaller than 100 Myrs. Other examples are K2-33b, V1298 Tauri b and AU Microscopium b. Of these systems DS Tuc is the brightest and it is a good target for atmospheric characterization with JWST. The planet is a super-Neptune or sub-Saturn. The planet might be an inflated planet with an upper mass limit of 20. DS Tuc Ab will be observed by ESA's CHEOPS mission to characterize the planet.
The planet DS Tucanae Ab has a low orbital obliquity. This means that the orbital plane of this planet aligns with the stellar equator of the star. This is unusual for a short period planet. Many short period planets show high orbital obliquity, which was taken as a sign of the scattering of the planet into this short period orbit. It can also be interpreted as the formation of a planet in an inner disk with an axial tilt. But these previous measurements of orbital obliquity were made for giant planets around mature stars. DS Tucanae Ab is a relative small young planet. This result suggests that DS Tucanae Ab formed in a smooth disk that was not perturbed by the stellar companion DS Tucanae B. DS Tucanae Ab might be therefore a good target to study in-situ planet-formation of short-period planets.