AB Doradus

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This article is about the pre-main-sequence quadruple star system in the constellation Doradus. For the group of several dozen stars that moves with it, see AB Doradus moving group.
AB Doradus A/B/C
ESO - Near-Infrared Image of AB Doradus A and its Companion.jpg
AB Doradus with the orbit of C in yellow
Observation data
Epoch J2000      Equinox J2000
Constellation Dorado
Right ascension 05h 28m 44.828s
Declination −65° 26′ 54.85″
Apparent magnitude (V) 6.98−7.06[1]/13.0
Spectral type K1Vp + dM3-4e + M8
U−B color index +0.37
B−V color index +0.86±0.02[1]
Variable type Flare star
Radial velocity (Rv) +28.0 km/s
Proper motion (μ) RA: 32.14 mas/yr
Dec.: 150.97 mas/yr
Parallax (π) 66.92 ± 0.54 mas
Distance 48.7 ± 0.4 ly
(14.9 ± 0.1 pc)
Companion AB Doradus B
Semi-major axis (a) 135 AU"
Companion AB Doradus C
Period (P) 11.75 yr
Semi-major axis (a) 2.3 AU"
Mass 0.86[2] M
Radius 0.96±0.06[2] R
Temperature 5,250[3] K
Rotation 0.5148 days[3]
Age 50[4] Myr
Other designations
AB Dor, CD -65°332, HD 36705, HIP 25647.
Database references

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.

The primary star in this system spins at a rate 50 times that of the Sun, and consequently has a strong magnetic field.[6] 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.[7]

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.[8]

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.[9] It is likely that all of these stars formed in the same giant molecular cloud.


  1. ^ a b 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. 
  2. ^ a b 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:1501.05846Freely accessible, Bibcode:2015ApJ...802...62D, doi:10.1088/0004-637X/802/1/62, 62. 
  3. ^ a b 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 
  4. ^ K. L. Luhman, John R. Stauffer, E. E. Mamajek (2005). "The Age of AB Dor". Astrophysical Journal. 628 (1): L69–L72. arXiv:astro-ph/0510665Freely accessible. Bibcode:2005ApJ...628L..69L. doi:10.1086/432617. 
  5. ^ a b Azulay, R.; et al. (June 2015), "Dynamical masses of the low-mass stellar binary AB Doradus B", Astronomy & Astrophysics, 578: 9, arXiv:1504.02766Freely accessible, Bibcode:2015A&A...578A..16A, doi:10.1051/0004-6361/201525704, A16. 
  6. ^ JR Minkel (2001-12-11). "Shimmying Star May Shed Light on Forces at Work in the Sun". Scientific American. Retrieved 2006-06-25. 
  7. ^ A. C. Cameron; J. F. Donati. "Christmas Star Does the Twist". PPARC. Retrieved 2006-08-25.  (The AB Dor Picture Gallery)
  8. ^ "Weighing the Smallest Stars". ESO. 2005-01-19. Archived from the original on 20 August 2006. Retrieved 2006-08-13. 
  9. ^ 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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