AB Doradus

AB Doradus is a pre-main-sequence quadruple[5] star system in the constellation Dorado. The primary is a flare star that shows periodic increases in activity.

This article is about the star system in the constellation Doradus. For the group of stars that moves with it, see AB Doradus moving group.
AB Doradus

AB Doradus with the orbit of C in yellow
Observation data
Epoch J2000      Equinox J2000
Constellation Dorado
Right ascension  05h 28m 44.8489s[1]
Declination −65° 26′ 54.946″[1]
Apparent magnitude (V) 6.98−7.06[2] / 13.0[3]
Characteristics
AB Dor AC
Spectral type K0V[4] + M8
U−B color index +0.37
B−V color index +0.86±0.02[2]
Variable type Flare star
AB Dor B
Spectral type M5 + M5-6[5]
Astrometry
Radial velocity (Rv)32.40 ± 2.2[6] km/s
Proper motion (μ) RA: 33.16[7] mas/yr
Dec.: 150.83[7] mas/yr
Parallax (π)65.93 ± 0.57[7] mas
Distance49.5 ± 0.4 ly
(15.2 ± 0.1 pc)
Absolute magnitude (MV)5.86[8]
Orbit[5]
PrimaryAB Dor Ba
CompanionAB Dor Bb
Period (P)0.986 ± 0.008 yr
Semi-major axis (a)0.052 ± 0.002″
Eccentricity (e)0.6 ± 0.1
Inclination (i)121 ± 5°
Longitude of the node (Ω)270 ± 15°
Periastron epoch (T)2003.68 ± 0.05
Argument of periastron (ω)
(secondary)		54 ± 20°
Orbit[9]
PrimaryAB Dor A
CompanionAB Dor C
Period (P)12.895 yr
Semi-major axis (a)0.304″
Eccentricity (e)0.281
Inclination (i)63.0°
Longitude of the node (Ω)159.2°
Periastron epoch (T)B 1991.822
Argument of periastron (ω)
(secondary)		157.3°
Details
AB Dor A
Mass0.86[10] M☉
Radius0.96±0.06[10] R☉
Temperature5,250[11] K
Rotation0.5148 days[11]
Age50[12] Myr
AB Dor Ba
Mass0.28 ± 0.05[5] M☉
AB Dor Bb
Mass0.25 ± 0.05[5] M☉
Other designations
AB Dor, CD−65° 332, HD 36705, HIP 25647
Database references
SIMBADdata
ARICNSdata

The primary star in this system spins at a rate 50 times that of the Sun, and consequently has a strong magnetic field.[13] It has a greater number of star spots than the Sun. These can cause the luminosity of the star to appear to vary over each orbital cycle. Measurements of the spin rate of this star at its equator have shown that it varies over time due to the effect of this magnetic field.[14]

The system has four components consisting of a pair of binary star systems separated by an angle of about 9″.[5] The binary star AB Doradus Ba/Bb orbits the primary AB Doradus A at an average distance of 135 astronomical units (AUs). AB Doradus C, is a close-in companion that orbits the primary at a distance of 2.3 AU, and has an orbital period of 11.75 years. The latter star is among the lowest-mass stars ever found. At an estimated mass 93 times Jupiter's, it is near the limit of 75–83 Jupiter masses below which it would be classified as a brown dwarf.[15]

This system is a member of the eponymous AB Doradus Moving Group, a loose stellar association of about 30 stars that are all approximately the same age and moving in the same general direction.[16] It is likely that all of these stars formed in the same giant molecular cloud.

References
  1. Gaia Collaboration (2016). "Gaia Data Release 1". Astronomy & Astrophysics. 595: A2. arXiv:1609.04172. Bibcode:2016A&A...595A...2G. doi:10.1051/0004-6361/201629512.
  2. Innis, J. L.; et al. (May 2008), "Recent CCD Photometry of AB Dor, and a Comment on the Long-term Activity Cycle", Information Bulletin on Variable Stars (5832): 1, Bibcode:2008IBVS.5832....1I.
  3. "NAME AB Dor B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 19 July 2017.
  4. Torres, C. A. O.; et al. (December 2006), "Search for associations containing young stars (SACY). I. Sample and searching method", Astronomy and Astrophysics, 460 (3): 695–708, arXiv:astro-ph/0609258, Bibcode:2006A&A...460..695T, doi:10.1051/0004-6361:20065602.
  5. Azulay, R.; et al. (June 2015), "Dynamical masses of the low-mass stellar binary AB Doradus B", Astronomy & Astrophysics, 578: 9, arXiv:1504.02766, Bibcode:2015A&A...578A..16A, doi:10.1051/0004-6361/201525704, A16.
  6. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
  7. van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  8. Holmberg, J.; et al. (July 2009). "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics". Astronomy and Astrophysics. 501 (3): 941–947. arXiv:0811.3982. Bibcode:2009A&A...501..941H. doi:10.1051/0004-6361/200811191.
  9. "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Retrieved 19 June 2017.
  10. Drake, Jeremy J.; et al. (March 2015), "X-Ray Evidence for a Pole-dominated Corona on AB Dor", The Astrophysical Journal, 802 (1): 11, arXiv:1501.05846, Bibcode:2015ApJ...802...62D, doi:10.1088/0004-637X/802/1/62, 62.
  11. Strassmeier, Klaus G. (September 2009), "Starspots", The Astronomy and Astrophysics Review, 17 (3): 251–308, Bibcode:2009A&ARv..17..251S, doi:10.1007/s00159-009-0020-6
  12. K. L. Luhman, John R. Stauffer, E. E. Mamajek (2005). "The Age of AB Dor". Astrophysical Journal. 628 (1): L69–L72. arXiv:astro-ph/0510665. Bibcode:2005ApJ...628L..69L. doi:10.1086/432617.
  13. JR Minkel (2001-12-11). "Shimmying Star May Shed Light on Forces at Work in the Sun". Scientific American. Retrieved 2006-06-25.
  14. A. C. Cameron; J. F. Donati. "Christmas Star Does the Twist". PPARC. Archived from the original on 2015-09-23. Retrieved 2006-08-25. (The AB Dor Picture Gallery)
  15. "Weighing the Smallest Stars". ESO. 2005-01-19. Retrieved 2006-08-13.
  16. B. Zuckerman, I. Song, M. S. Bessell (2005). "The AB Doradus Moving Group". The Astrophysical Journal. 613 (1): L65–L68. Bibcode:2004ApJ...613L..65Z. doi:10.1086/425036.
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