DS Tucanae
Binary star system in the constellation of Tucana
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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]
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| 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 | A |
| B | |
| Ab | |
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]
Together with the red dwarf 2MASS J23321028–6926537, DS Tucanae might be a triple stellar system. This star shares a similar distance and similar proper motions. It is separated 113,000 astronomical units from DS Tuc.[16]
Physical properties
In 1996, analysis of the Hipparcos data showed that the star is a variable star. It was given its variable star designation in 1999.[17]
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.[18]
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
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | <14.4[9] M🜨 | 0.18+0.13 −0.12 |
8.138268 | — | 88.73+0.18 −0.17[9]° |
5.70±0.17 R🜨 |
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🜨.[12] DS Tuc Ab will be observed by ESA's CHEOPS mission to characterize the planet.[19]
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.[20][21] DS Tucanae Ab might therefore be a good target to study in-situ planet-formation of short-period planets.