Mu1 Gruis

Mu¹ Gruis, Latinized from μ¹ Gruis, is a binary star^[3] system in the southern constellation of Grus. It is visible to the naked eye with a combined apparent visual magnitude of 4.79.^[2] The distance to this system, as determined using an annual parallax shift of 11.44 mas as seen from the Earth,^[8] is around 275 light years. It is drifting closer with a heliocentric radial velocity of −5 km/s.^[1]

For other stars with this Bayer designation, see μ Gruis.

Mu¹ Gruis

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Grus
Right ascension	22h 15m 36.93338s[1]
Declination	−41° 20′ 48.3558″[1]
Apparent magnitude (V)	4.79[2] (5.20 + 6.68)[3]
Characteristics
Spectral type	G8 III + G[4]
U−B color index	+0.47[2]
B−V color index	+0.80[2]
Astrometry
Radial velocity (Rv)	−4.82±1.54[1] km/s
Proper motion (μ)	RA: +30.774[1] mas/yr Dec.: +42.645[1] mas/yr
Parallax (π)	13.5115±0.2846 mas[1]
Distance	241 ± 5 ly (74 ± 2 pc)
Absolute magnitude (MV)	+0.17[5]
Orbit[6]
Period (P)	19.04+0.16 −0.18 yr
Semi-major axis (a)	0.168+0.003 −0.002″
Eccentricity (e)	0.561+0.025 −0.020
Inclination (i)	65.69+0.44 −0.53°
Longitude of the node (Ω)	104.2+1.6 −1.8°
Periastron epoch (T)	1996.35+0.17 −0.18
Argument of periastron (ω) (secondary)	92.61+0.67 −0.54°
Details
A
Radius	9.3+1.4 −1.3[1] R☉
Luminosity	66.9+1.8 −1.6[1] L☉
Temperature	5,422+423 −377[1] K
Other designations
μ1 Gru, CD−41°14810, FK5 3777, HD 211088, HIP 109908, HR 8486, SAO 231055, WDS J22156-4121[7]
Database references
SIMBAD	data

The pair orbit each other with a period of 19 years and an eccentricity of 0.56.^[6] The yellow-hued primary component is an evolved giant star with stellar classification of G III^[4] and visual magnitude 5.20.^[3] With the supply of hydrogen at its core exhausted, it cooled and expanded; at present it has nine^[1] times the girth of the Sun. The star is radiating 67 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 5,422 K.^[1]

The secondary component is magnitude 6.68 and classed as a G-type star,^[3] although its color index and absolute magnitude suggest it is of type A6.^[6]