DS Tucanae

DS Tucanae imaged with the NTT. DS Tucanae A is on the right and DS Tucanae B is on the left.
Observation data Epoch J2000.0       Equinox J2000.0
Constellation	Tucana
DS Tucanae A
Right ascension	23h 39m 39.48081s [1]
Declination	−69° 11′ 44.7077″ [1]
Apparent magnitude (V)	8.47 [2]
DS Tucanae B
Right ascension	23h 39m 39.26965s [3]
Declination	−69° 11′ 39.4936″ [3]
Apparent magnitude (V)	9.84 [4]
Characteristics
Spectral type	G6V+K3V [4]
Variable type	RS CVn [5]
Astrometry
A
Radial velocity (Rv)	7.20 [6] km/s
Proper motion (μ)	RA: 79.529 [1]  mas/ yr Dec.: −67.551 [1]  mas/ yr
Parallax (π)	22.6367 ± 0.0150  mas [1]
Distance	144.08 ± 0.10  ly (44.18 ± 0.03  pc)
B
Radial velocity (Rv)	5.32 [7] km/s
Proper motion (μ)	RA: 78.133 [3]  mas/ yr Dec.: −65.845 [3]  mas/ yr
Parallax (π)	22.6524 ± 0.0125  mas [3]
Distance	143.98 ± 0.08  ly (44.15 ± 0.02  pc)
Details
DS Tucanae A
Mass	1.01±0.06 [8]  M☉
Radius	0.964±0.029 [8]  R☉
Luminosity	0.725±0.013 [8]  L☉
Temperature	5,428±80 [8]  K
Rotational velocity (v sin i)	27.75+1.73 −1.54 [9] km/s
Age	45±4 [8]  Myr
DS Tucanae B
Mass	0.84±0.06 [8]  M☉
Radius	0.864±0.036 [8]  R☉
Luminosity	0.327±0.010 [8]  L☉
Temperature	4,700±90 [8]  K
Age	45±4 [8]  Myr
Other designations
DS Tuc, HD 222259, CCDM J23397-6912AB, CD−69°2106, HIP 116748, WDS J23397-6912AB, TIC 410214986, TOI 200
Database references
SIMBAD	AB
	A
	B
	Ab

DS Tucanae (HD 222259) is a binary star system 144 light years away in the constellation of Tucana. It has an apparent visual magnitude of 8.5, ^[8] and is a RS Canum Venaticorum variable. ^[5] The system is notable for being young as a member of the 45 Myr old Tucana-Horologium moving group ^[10] and for the primary star hosting the confirmed exoplanet DS Tucanae Ab, discovered by THYME, using TESS. ^{[11] [8] [12] [13]}

Stellar system

DS Tucanae is a visual binary. ^[4] The binary consists of a G6V primary and a K3V secondary separated by 5 ″. ^[15] 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. ^[8]

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. ^[12] The primary star is emitting a frequent and powerful (up to 5-8×10³⁴ ergs) X-ray flares. ^[16]

Both components of the binary are main sequence stars. The primary has a mass very similar to the Sun, but slightly cooler and smaller, meaning it is only 72% as luminous as the Sun. The secondary is only 84% as massive as the Sun and only 33% as luminous.

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 Microscopii 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. ^[8] The planet might be an inflated planet with an upper mass limit of 20 M_E. ^[12] DS Tuc Ab will be observed by ESA's CHEOPS mission to characterize the planet. ^[17]

The planet DS Tucanae Ab has a low orbital obliquity (λ = 2.93 °+0.88 °
−0.87 ° or λ = 12°±13°). 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 relatively small young planet. This suggests that DS Tucanae Ab formed in a smooth disk that was not perturbed by the stellar companion DS Tucanae B. ^{[18] [19]} DS Tucanae Ab might therefore be a good target to study in-situ planet-formation of short-period planets.

References