Gamma Gruis

"Aldhanab" redirects here; not to be confused with Deneb.

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]

Gamma Gruis

Location of γ Gruis (circled) near the center
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]

See also

• Traditional Chinese star names#Grus