DS Tucanae

DS Tucanae (HD 222259) is a binary star system in the constellation of Tucana. It has an apparent visual magnitude of 8.5,[7] and is a RS Canum Venaticorum variable.[4] The system is notable for being young as a member of the 45 Myr old Tucana-Horologium moving group[8] and for the primary star hosting the confirmed exoplanet DS Tucanae Ab, discovered by TESS.[9][7][10][11]

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	23^h 39^m 39.48096^s[1]
Declination	−69° 11′ 44.7093″[1]
Apparent magnitude (V)	8.47[2]
DS Tucanae B
Right ascension	23^h 39^m 39.26995^s[1]
Declination	–69° 11′ 39.4950″[1]
Apparent magnitude (V)	9.84[3]
Characteristics
Spectral type	G6V+K3V[3]
Variable type	RS CVn[4]
Astrometry
A
Radial velocity (Rv)	7.20[5] km/s
Proper motion (μ)	RA: 79.464[5] mas/yr Dec.: -67.440[5] mas/yr
Parallax (π)	22.6663 ± 0.0354[5] mas
Distance	143.9 ± 0.2 ly (44.12 ± 0.07 pc)
B
Radial velocity (Rv)	6.1[6] km/s
Proper motion (μ)	RA: 78.022[5] mas/yr Dec.: -65.746[6] mas/yr
Parallax (π)	22.6504 ± 0.0297[6] mas
Distance	144.0 ± 0.2 ly (44.15 ± 0.06 pc)
Details
DS Tucanae A
Mass	1.01±0.06[7] M☉
Radius	0.964±0.029[7] R☉
Luminosity	0.725±0.013[7] L☉
Temperature	5428±80[7] K
Age	45±4[7] Myr
DS Tucanae B
Mass	0.84±0.06[7] M☉
Radius	0.864±0.036[7] R☉
Luminosity	0.327±0.010[7] L☉
Temperature	4700±90[7] K
Age	45±4[7] 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

Stellar System

DS Tucanae is a visual binary.[3] The binary consists of a G6V primary and a K3V secondary separated by 5".[12] 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.[7]

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.[10]

Planetary System

The DS Tuc A planetary system[7][10]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	<1.3 MJ	0.18+0.13 −0.12	8.138268	—	89.5+0.34 −0.41°	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 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.[7] The planet might be an inflated planet with an upper mass limit of 20 M_⊕.[10] DS Tuc Ab will be observed by ESA's CHEOPS mission to characterize the planet.[13]

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 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.[14][15] DS Tucanae Ab might be therefore a good target to study in-situ planet-formation of short-period planets.

References

1. Gaia Collaboration (2018-08-01). "Gaia Data Release 2 - Summary of the contents and survey properties". Astronomy & Astrophysics. 616: A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. ISSN 0004-6361.
2. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (March 2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H. ISSN 0004-6361.
3. Torres, G. (August 1988). "Visual Measurements of Southern Double Stars - Part Three". Astrophysics and Space Science. 147 (2): 257–266. Bibcode:1988Ap&SS.147..257T. doi:10.1007/BF00645670. ISSN 0004-640X.
4. Samus', N. N.; Goranskii, V. P.; Durlevich, O. V.; Zharova, A. V.; Kazarovets, E. V.; Kireeva, N. N.; Pastukhova, E. N.; Williams, D. B.; Hazen, M. L. (July 2003). "An Electronic Version of the Second Volume of the General Catalogue of Variable Stars with Improved Coordinates". Astronomy Letters. 29 (7): 468–479. Bibcode:2003AstL...29..468S. doi:10.1134/1.1589864. ISSN 1063-7737.
5. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
6. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
7. Newton, Elisabeth R.; et al. (July 2019). "TESS Hunt for Young and Maturing Exoplanets (THYME): A Planet in the 45 Myr Tucana-Horologium Association" (PDF). The Astrophysical Journal Letters. 880 (1): L17. Bibcode:2019ApJ...880L..17N. doi:10.3847/2041-8213/ab2988. ISSN 0004-637X.
8. Zuckerman, B.; Webb, R. A. (2000-06-01). "Identification of a Nearby Stellar Association in theHipparcos Catalog: Implications for Recent, Local Star Formation". The Astrophysical Journal. 535 (2): 959. arXiv:astro-ph/0002461. Bibcode:2000ApJ...535..959Z. doi:10.1086/308897. ISSN 0004-637X.
9. Albright, Charlotte. "Dartmouth Astronomer on Leading Discovery of a New Planet | Dartmouth News". news.dartmouth.edu. Retrieved 2019-12-18.
10. Benatti, S.; Nardiello, D.; Malavolta, L.; Desidera, S.; Borsato, L.; Nascimbeni, V.; Damasso, M.; D'Orazi, V.; Mesa, D.; Messina, S.; Esposito, M.; Bignamini, A.; Claudi, R.; Covino, E.; Lovis, C.; Sabotta, S. (October 2019). "A possibly inflated planet around the bright young star DS Tucanae A". Astronomy & Astrophysics. 630: A81. arXiv:1904.01591. Bibcode:2019A&A...630A..81B. doi:10.1051/0004-6361/201935598. ISSN 0004-6361.
11. "DS Tuc A b". exoplanetarchive.ipac.caltech.edu. Retrieved 2019-12-18.
12. Torres, C. a. O.; Quast, G. R.; Silva, L. da; Reza, R. de la; Melo, C. H. F.; Sterzik, M. (2006-12-01). "Search for associations containing young stars (SACY) - I. Sample and searching method". Astronomy & Astrophysics. 460 (3): 695–708. arXiv:astro-ph/0609258. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602. ISSN 0004-6361.
13. "AO-1 Programmes - CHEOPS Guest Observers Programme - Cosmos". www.cosmos.esa.int. Retrieved 2019-12-18.
14. Montet, Benjamin T.; Feinstein, Adina D.; Luger, Rodrigo; Bedell, Megan E.; Gully-Santiago, Michael A.; Teske, Johanna K.; Xuesong Wang, Sharon; Butler, R. Paul; Flowers, Erin; Shectman, Stephen A.; Crane, Jeffrey D. (2020). "The Young Planet DS Tuc Ab has a Low Obliquity". The Astronomical Journal. 159 (3): 112. arXiv:1912.03794. Bibcode:2020AJ....159..112M. doi:10.3847/1538-3881/ab6d6d.
15. Zhou, G.; Winn, J. N.; Newton, E. R.; Quinn, S. N.; Rodriguez, J. E.; Mann, A. W.; Rizzuto, A. C.; Vanderburg, A. M.; Huang, C. X.; Latham, D. W.; Teske, J. K. (December 2019). "A well aligned orbit for the 45 Myr old transiting Neptune DS Tuc Ab". arXiv:1912.04095 [astro-ph.EP].