Epsilon Gruis

ε Gruis, Latinised as Epsilon Gruis, is a blue-white hued star in the southern constellation of Grus. It is visible to the naked eye, having an apparent visual magnitude of 3.5.^[2] Based upon an annual parallax shift of 25.30 mas as measured from Earth,^[1] it is located around 129 light years from the Sun. The system may be moving closer to the Sun with a radial velocity of about −0.4 km/s.^[4]

Epsilon Gruis

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Grus
Right ascension	22h 48m 33.29833s[1]
Declination	−51° 19′ 00.7001″[1]
Apparent magnitude (V)	3.466[2]
Characteristics
Spectral type	A2 IVn[3]
B−V color index	0.09[2]
Astrometry
Radial velocity (Rv)	−0.4±2.1[4] km/s
Proper motion (μ)	RA: +108.43[1] mas/yr Dec.: −64.83[1] mas/yr
Parallax (π)	25.30±0.48 mas[1]
Distance	129 ± 2 ly (39.5 ± 0.7 pc)
Absolute magnitude (MV)	+0.52[5]
Details
Mass	1.85[6] M☉
Surface gravity (log g)	3.47±0.14[6] cgs
Temperature	8,685±295[6] K
Metallicity [Fe/H]	−0.16[3] dex
Rotational velocity (v sin i)	235.1±11.8[5] km/s
Age	249[6] Myr
Other designations
ε Gru, CD−51°13389, FK5 860, GJ 9796, HD 215789, HIP 112623, HR 8675, SAO 247593[7]
Database references
SIMBAD	data

This is an A-type subgiant of spectral type A2IVn,^[3] a star that has used up its core hydrogen and has begun to expand off the main sequence. At the estimated age of 249 million years,^[6] it is spinning rapidly with a projected rotational velocity of 235 km/s.^[5] This is giving the star an oblate shape with an equatorial bulge that is an estimated 18% larger than the polar radius.^[8] The star displays an infrared excess, suggesting the presence of a circumstellar disk of orbiting dust.^[9]

Epsilon Gruis is suspected of having a moderately active^[10] close companion,^[11] which is most likely the source of the weak X-ray emission from these coordinates with a luminosity of 1.3×10²⁸ erg s⁻¹.^[10]