Gamma Gruis
Star in the constellation Grus
From Wikipedia, the free encyclopedia
Gamma Gruis or γ Gruis, formally named Aldhanab (/ˈældənæb/),[13] is a star in the southern constellation of Grus (it once belonged to the Ptolemaic constellation Piscis Austrinus). With an apparent visual magnitude of 3.0,[2] it is the third-brightest star in Grus. Based upon parallax measurements, this star is located at a distance of roughly 211 light-years (65 parsecs) from the Sun.[1]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Grus |
| Right ascension | 21h 53m 55.72620s[1] |
| Declination | −37° 21′ 53.4790″[1] |
| Apparent magnitude (V) | 3.003[2] |
| Characteristics | |
| Spectral type | B8 III[3] or B8IV-Vs[4] |
| U−B color index | −0.307[2] |
| B−V color index | −0.121[2] |
| Astrometry | |
| Radial velocity (Rv) | −2.1[5] km/s |
| Proper motion (μ) | RA: +98.07[1] mas/yr Dec.: −13.22[1] mas/yr |
| Parallax (π) | 15.45±0.67 mas[1] |
| Distance | 211 ± 9 ly (65 ± 3 pc) |
| Absolute magnitude (MV) | −1.05[6] |
| Details | |
| Mass | 3.06[7] M☉ |
| Radius | 4.5[8] R☉ |
| Luminosity | 373[6] L☉ |
| Surface gravity (log g) | 3.79[7] cgs |
| Temperature | 12,520[9] K |
| Rotation | 4.987[10] d |
| Rotational velocity (v sin i) | 57[11] km/s |
| Age | 75[7] Myr |
| Other designations | |
| γ Gru, Gamma Gru, CD−37°9119, FK5 822, GC 30640, HD 207971, HIP 108085, HR 8353, SAO 213374[12] | |
| Database references | |
| SIMBAD | data |
Nomenclature
γ Gruis (Latinised to Gamma Gruis) is the system's Bayer designation.
It bore the traditional Arabic name Al Dhanab, from the Arabic الذنب al-dhanab "the tail" (of the Southern Fish)[14]when it was still part of Piscis Austrinus with the Bayer designation κ Piscis Austrini (Kappa Piscis Austrini). In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN approved the name Aldhanab for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[13]
In Chinese, 敗臼 (Bài Jiù), meaning Decayed Mortar, refers to an asterism consisting of Gamma Gruis, Lambda Gruis, Gamma Piscis Austrini and 19 Piscis Austrini.[16] Consequently, the Chinese name for Gamma Gruis itself is 敗臼一 (Bài Jiù yī, English: the First Star of Decayed Mortar.)[17]
Properties
Analysis of the spectrum by N. Houk in 1979 shows it to match a stellar classification of B8 III,[3] with the luminosity class of III indicating this is a giant star that has exhausted the supply of hydrogen at its core and evolved away from the main sequence. R. O. Gray and R. F. Garrison in 1989 found a less evolved class of B8IV-Vs.[4] The luminosity of Gamma Gruis is around 390 times that of the Sun, with a significant portion of the energy emission being in the ultraviolet.[18] Its outer envelope has an effective temperature of 12,520 K,[9] which gives the star a blue-white hue. Gamma Gruis is rotating relatively rapidly with a projected rotational velocity of 57 km s−1.[11] By way of comparison, the Sun has an azimuthal velocity along its equator of just 2 km s−1.
Based upon analysis of data collected during the Hipparcos mission, this star may have a proper motion companion that is causing gravitational perturbation of Gamma Gruis.[19] In addition, there is a star sharing common proper motion and similar distance with Gamma Gruis, and thus is believed to the gravitationally bound. It has a projected separation of 162,100 astronomical units (0.786 pc; 2.563 ly), and a mass and radius around 30% that of the Sun. They likely make a binary system.[20]