Beta Arae

Beta Arae is the brightest star in the constellation of Ara. This is a very luminous, relatively young red supergiant with an apparent visual magnitude of 2.84 and an absolute magnitude of −3.494.^[2][8] Its name is a Bayer designation that is Latinized from β Arae, and abbreviated Beta Ara or β Ara. Based on a photogeometric estimation method, it is 710 light-years away,^[7] a distance of which interstellar extinction in the line of sight reduces its apparent magnitude by 0.193 magnitudes.^[9]

β Arae

Location of β Arae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ara
Right ascension	17h 25m 17.989s[1]
Declination	−55° 31′ 47.57″[1]
Apparent magnitude (V)	2.84[2]
Characteristics
Evolutionary stage	Red supergiant
Spectral type	K0/1Ib[3]
U−B color index	+1.56[4]
B−V color index	+1.46[4]
Astrometry
Radial velocity (Rv)	−0.3±0.2[5] km/s
Proper motion (μ)	RA: −8.51 mas/yr[6] Dec.: −25.24 mas/yr[6]
Parallax (π)	4.5601±0.2077 mas[1]
Distance	714+39 −34 ly (218.8+12.0 −10.4 pc)[7]
Absolute magnitude (MV)	−3.494[8]
Details[9]
Mass	5.89±0.07 or 7.89±0.4 M☉
Radius	141.4±6.6 R☉
Luminosity	5,774±535 L☉
Surface gravity (log g)	0.97±0.06 cgs
Temperature	4,232±17 K
Metallicity [Fe/H]	0.5±0.1 dex
Rotational velocity (v sin i)	5.4±1.0[5] km/s
Age	50.1±4.4[10] Myr
Other designations
CPD−55°8100, FK5 645, GC 23515, HD 157244, HIP 85258, HR 6461, SAO 244725, PPM 345989[11]
Database references
SIMBAD	data

Characteristics

The spectrum of this star matches a stellar classification of K0/1 Ib,^[3] with the luminosity class notation 'Ib' indicating that the star is a supergiant. It has an age estimated at 50 million years,^[10] having spent much of its life as a B-type star.^[12] Currently, it has expanded to 141 times the Sun's size and is 5,800 times more luminous.^[9] Beta Arae is radiating energy from its outer envelope at an effective temperature of 4,200 K, which causes it to take on the orange hue of a K-type star.^[13] This enlarged star appears to be rotating slowly with a projected rotational velocity of about 5 km/s.^[5] The abundance of elements other than hydrogen and helium, its metallicity, is more than three times that of the Sun.^[5][a]

Nomenclature

Beta Arae is the star's Bayer designation. Other designations include HD 157244 (from the Henry Draper Catalogue), HIP 85258 (from the Hipparcos catalogue) and HR 6461 (from the Bright Star Catalogue).^[11]

Rarely, this star is called Vasat-ül-cemre a Turkisation of Arabic وسط الجمر (wasaṭ al-jamar), meaning "middle of the embers."^[14] The constellation is named in Arabic المجمرة (al-mijmarah), meaning brazier/incense-burner.^[15] In Chinese, 杵 (Chǔ), meaning Pestle, refers to an asterism of β, σ and α Arae.^[16] The Chinese name for β Arae is 杵三 (Chǔ sān, English: the Third Star of Pestle.)^[17]

Notes

1. The abundance is estimated by taking [Fe/H] to the power of ten:
             10^[Fe/H] = 10^+0.5 = 3.1