Beta Gruis
Star in the constellation of Grus
From Wikipedia, the free encyclopedia
Beta Gruis (β Gruis, abbreviated Beta Gru, β Gru), formally named Tiaki /tiˈɑːki/,[13] is the second brightest star in the southern constellation of Grus. It was once considered the rear star in the tail of the constellation of the (Southern) Fish, Piscis Austrinus: it, with Alpha, Delta, Theta, Iota, and Lambda Gruis, belonged to Piscis Austrinus in medieval Arabic astronomy.[14]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Grus |
| Right ascension | 22h 42m 40.05027s[1] |
| Declination | −46° 53′ 04.4752″[1] |
| Apparent magnitude (V) | 2.146[2] (2.0 - 2.3[3]) |
| Characteristics | |
| Evolutionary stage | AGB[4] |
| Spectral type | M4.5 III[5] |
| U−B color index | +1.757[2] |
| B−V color index | +1.620[2] |
| Variable type | SRb[3] |
| Astrometry | |
| Radial velocity (Rv) | +1.6[6] km/s |
| Proper motion (μ) | RA: +135.16[1] mas/yr Dec.: −4.38[1] mas/yr |
| Parallax (π) | 18.43±0.42 mas[1] |
| Distance | 177 ± 4 ly (54 ± 1 pc) |
| Absolute magnitude (MV) | −1.61±0.052[7] |
| Details | |
| Mass | 2.4[8] M☉ |
| Radius | 154[9] R☉ |
| Luminosity | 3,221±242[9] L☉ |
| Surface gravity (log g) | 0.4[10] cgs |
| Temperature | 3,508±125[9] K |
| Metallicity [Fe/H] | 0.0[10] dex |
| Age | 450[11] Myr |
| Other designations | |
| Tiaki, Beta Gru, CD−47 14308, FK5 856, HR 8636, HD 214952, HIP 112122, SAO 231258.[12] | |
| Database references | |
| SIMBAD | data |
Nomenclature
β Gruis (Latinised to Beta Gruis) is the star's Bayer designation.
It bore the traditional Tuamotuan name of Tiaki.[15] In 2016, the IAU organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN approved the name Tiaki for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[13]
In Chinese, 鶴 (Hè), meaning Crane, refers to an asterism consisting of Beta Gruis, Alpha Gruis, Epsilon Gruis, Eta Gruis, Delta Tucanae, Zeta Gruis, Iota Gruis, Theta Gruis, Delta² Gruis and Mu¹ Gruis.[17] Consequently, Beta Gruis itself is known as 鶴二 (Hè èr, English: Second Star of the Crane).[18] The Chinese name gave rise to another English name, Ke.[19]
Properties
Beta Gruis is a red giant star[3] on the asymptotic giant branch[4] with an estimated mass of about 2.4 times that of the Sun[20] and a surface temperature of approximately 3,500 K, just over half the surface temperature of the Sun.[9] This low temperature accounts for the dull red color of an M-type star. The total luminosity is about 3,200 times that of the Sun, and it has 150 times the Sun's radius.[9]
It is one of the brightest stars at infrared and near-infrared wavelenghts. At the K band, it is the fifth-brightest star in the night sky.[21]
Alan William James Cousins announced that Beta Gruis is a variable star in 1952.[22] Beta Gruis is a semiregular variable (SRb) star that varies in magnitude by about 0.4. It varies between intervals when it displays regular changes with a 37-day periodicity and times when it undergoes slow irregular variability.[3]