Beta Arae
Beta Arae (β Ara, β Arae), the brightest star in the constellation of Ara, is a very luminous, relatively young, giant star with an apparent visual magnitude of 2.8 (rounded). Parallax measurements place it at roughly 650 light-years (200 parsecs) from Earth.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ara |
| Right ascension | 17h 25m 17.98835s |
| Declination | −55° 31′ 47.5868″ |
| Apparent magnitude (V) | 2.84 |
| Characteristics | |
| Spectral type | K3 Ib-II |
| U−B color index | +1.56 |
| B−V color index | +1.46 |
| Astrometry | |
| Radial velocity (Rv) | −0.30±0.20 km/s |
| Proper motion (μ) | RA: −8.51 mas/yr Dec.: −25.24 mas/yr |
| Parallax (π) | 4.5601 ± 0.2077 mas |
| Distance | 720 ± 30 ly (219 ± 10 pc) |
| Absolute magnitude (MV) | −3.494 |
| Details | |
| Mass | 8.21 ,6.2~7.3 M☉ |
| Radius | 142; 92 R☉ |
| Luminosity | 5,636 L☉ |
| Surface gravity (log g) | 1.20 cgs |
| Temperature | 4,197 K |
| Metallicity [Fe/H] | −0.05 dex |
| Rotational velocity (v sin i) | 5.4±1.0 km/s |
| Age | 50.1±4.4 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The spectrum of this star matches a stellar classification of K3 Ib-IIa, with the luminosity class notation 'Ib-IIa' indicating that the star lies part way between a higher luminosity bright giant (IIa) and a lower luminosity supergiant (Ib). This represents two of the evolutionary stages that a massive star passes through after it has exhausted the hydrogen at its core. 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. This enlarged star appears to be rotating slowly with a projected rotational velocity of about 5 km/s. The abundance of elements other than hydrogen and helium, its metallicity, is more than three times that of the Sun.
Rarely, this star is called Vasat-ül-cemre a Turkisation of Arabic وسط الجمر (wasaṭ al-jamar), meaning "middle of the embers." The constellation is named in Arabic المجمرة (al-mijmarah), meaning brazier/incense-burner. In Chinese, 杵 (Chǔ), meaning Pestle, refers to an asterism of β, σ and α Arae. The Chinese name for β Arae is 杵三 (Chǔ sān, English: the Third Star of Pestle.)