Beta Tucanae

Beta Tucanae, Latinized from 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.^[11] The system is approximately 140 light years from Earth.

β^{1, 2} Tucanae

Location of β Tucanae group.
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Tucana
β1 Tuc (β Tuc AB)
Right ascension	00h 31m 32.6709s[1]
Declination	−62° 57′ 29.587″[1]
Apparent magnitude (V)	+4.37[2]
β2 Tuc (β Tuc CD)
Right ascension	00h 31m 33.4223s[1]
Declination	−62° 57′ 56.134″[1]
Apparent magnitude (V)	+4.54[2]
Characteristics
β1 Tuc
Spectral type	B9V[3]
β2 Tuc
Spectral type	A2V + A7V[4]
Astrometry
β1 Tuc
Parallax (π)	23.2596±0.2471 mas[5]
Distance	140 ± 1 ly (43.0 ± 0.5 pc)
β2 Tuc
Parallax (π)	19.5923±0.9674 mas[6]
Distance	166 ± 8 ly (51 ± 3 pc)
Details
β Tuc A
Mass	3.84[7] M☉
Radius	2.73[8] R☉
Luminosity	39[9] L☉
Surface gravity (log g)	4.37[9] cgs
Temperature	10,726[9] K
Rotational velocity (v sin i)	170[8] km/s
β Tuc B
Mass	0.40[7] M☉
β Tuc Ca
Mass	2.0[10] M☉
Radius	1.6[10] R☉
Temperature	9,200[10] K
β Tuc Cb
Mass	1.45[10] M☉
Radius	1.4[10] R☉
Temperature	7,000[10] K
β Tuc D
Mass	1.45[10] M☉
Radius	1.4[10] R☉
Temperature	7,000[10] K
Other designations
β Tuc, CPD−63°50, GC 625, HR 126, CCDM 00316-6258
β1: HD 2884, HIP 2484, SAO 248201
β2: HD 2885, HIP 2487, SAO 248202
Database references
	β1
	β2

β1, 2 Tucanae

Simulated image of the β Tucanae system

The two brightest stars, Beta¹ Tucanae and Beta² Tucanae, also referred to as Beta Tucanae A (or AB) and Beta Tucanae C (or CD), are 27 arcseconds, or at least 1100 astronomical units (AU) apart. They are both main sequence dwarfs, Beta¹ a blue-white B-type star with an apparent magnitude of +4.36, and Beta² a white A-type star with an apparent magnitude of +4.53.

Both of these bright stars are binaries. Beta Tucanae B is a magnitude +13.5 star which is a close companion to Beta¹, being 2.4 arcseconds, or at least 100 AU away.^[3] Beta Tucanae C is a close binary of components Ca and Cb, separated by 0.6 AU.^[10] The 6th magnitude Beta Tucanae D, is another A-type star which is separated by approximately 0.38 arcseconds (16 AU) from Beta Tucanae C.^[3]

β1 A

Sep = ~100 au

β1 B

Sep = ~1,200 au

β2 Ca

Sep = 0.59 au

β2 Cb

Sep = 22 au

β2 D

Sep = ~23,000 au

β3

Hierarchy of orbits in the β Tucanae system^[10]

β3 Tucanae

β³ Tucanae

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Tucana
Right ascension	00h 32m 43.905s[12]
Declination	−63° 01′ 53.40″[12]
Apparent magnitude (V)	+5.09[13]
Characteristics
Spectral type	A0V[14]
Astrometry
Radial velocity (Rv)	3.60[12] km/s
Proper motion (μ)	RA: +86.541[12] mas/yr Dec.: −50.115[12] mas/yr
Parallax (π)	21.6794±0.0683 mas[12]
Distance	150.4 ± 0.5 ly (46.1 ± 0.1 pc)
Absolute magnitude (MV)	+1.8[15]
Details
Mass	2.0[12] M☉
Radius	1.7[12] R☉
Luminosity	19[12] L☉
Surface gravity (log g)	4.14[12] cgs
Temperature	9,275[12] K
Metallicity [Fe/H]	0.17[16] dex
Rotational velocity (v sin i)	100[16] km/s
Other designations
CPD−63°52, GC 651, HD 3003, HIP 2578, HR 136, SAO 248208, CCDM 00327-6302
Database references
SIMBAD	data

Beta³ Tucanae is a suspected binary star which is separated from Beta¹ and Beta² 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 is not clear how tightly Beta³ 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.

In 1926, Beta³ Tucanae was reported to be a binary, with two components of magnitudes 5.7 and 6.1 separated by 0.1″,^[17] although more recent observations could not confirm this.^[14][18] At the separation of 0.1″ they would be separated by at least 4 au.^[19]

Beta³ Tucanae has an infrared excess, suggesting the presence a debris disk around the primary star.^[19]