Beta Tucanae

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β¹,² Tucanae
Tucana IAU.svg
Cercle rouge 100%.svg
Location of β Tucanae group.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Tucana
Right ascension 00h 31m 32.7s
Declination −62° 57′ 29″
Apparent magnitude (V) β¹: +4.36
β²: +4.53
Distance 140 ± 3 ly
(43 ± 1 pc)
Spectral type AB: A2V+B9V
Other designations
HR 126 + HR 126,
HD 2884 + HD 2885,
CP−63 50, HIP 2484 +
HIP 2487, SAO 248201 +
SAO 248202, GC 625,
CCDM 00316-6258

Beta Tucanae (β Tuc, β Tucanae) is a group of six stars which appear to be at least loosely bound into a system in the constellation Tucana. Three of the stars are luminous and distinct enough to have been given their own Bayer designations, β¹ Tucanae through β³ Tucanae.[1] The system is approximately 140 light years from Earth.

β¹,² Tucanae[edit]

The two brightest stars, Beta-1 Tucanae and Beta-2 Tucanae, also referred to as Beta Tucanae A and Beta Tucanae C, are 27 arcseconds, or at least 1100 astronomical units (AU) apart. They are both main sequence dwarfs, Beta-1 a blue-white B-type star with an apparent magnitude of +4.36, and Beta-2 a white A-type star with an apparent magnitude of +4.53.

Both of these bright stars have at least one closer main sequence companion. Beta Tucanae B is a magnitude +13.5 M3-type star which is a close companion to Beta-1, being 2.4 arcseconds, or at least 100 AU away. Beta-2's companion, the 6th magnitude Beta Tucanae D, is another A-type star which is separated by approximately 0.38 arcseconds (16 AU) from Beta-2.

β³ Tucanae[edit]

β³ Tucanae
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Tucana
Right ascension 00h 32m 43.8s
Declination −63° 01′ 52″
Apparent magnitude (V) combined: +5.07

AB: 5.8 + 6.0

Distance 152 ± 3 ly
(46 ± 1 pc)
Spectral type A0V+A2V
Other designations
HR 136, HD 3003,
CP−63 52, HIP 2578,
SAO 248208, GC 651,
CCDM 00327-6302

Beta-3 Tucanae is a binary star which is separated from Beta-1 and Beta-2 Tucanae by 9 arcminutes on the sky, which puts the two systems at least 23 000 astronomical units (AU) or 0.37 light years apart. It's not clear how tightly Beta-3 Tucanae is gravitationally bound to the rest of the β Tucanae system, but all the stars have similar distances from Earth and have the same proper motion on the sky, indicating they are gravitationally influencing each other to some degree.

Both components of the binary system are white A-type main sequence stars and they have apparent magnitudes of +5.8 and +6.0. They are separated by 0.1 arcseconds, or at least 4 astronomical units.

β Tucanae system[edit]

The stars in the system are poorly named, as their designations violate the convention for multiple stars. Beta-2 should be component B, but is C, while Beta-3 should be C, but is B.

Considering Beta-1a to be the central star, its binary companion, Beta-1b, orbits at a bit over three times Neptune's distance from the Sun. The Beta-2 pair is located over ten times further away. The pair is separated by less than the distance from the Sun to Uranus. The Beta-3 pair is much further out, at one-and-a-half times the distance of Proxima Centauri from the main Alpha Centauri pair. The Beta-3 pair are separated by less distance than the Sun and Jupiter.


  1. ^ Kaler, Jim. "Beta Tucanae". Stars. University of Illinois. Retrieved 2 May 2015.