Epsilon Gruis
Star in the constellation Grus
From Wikipedia, the free encyclopedia
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]
 | |
| 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☉ |
| Radius | 3.63[7] R☉ |
| Luminosity | 46.3[7] L☉ |
| Surface gravity (log g) | 3.47±0.14[6] cgs |
| Temperature | 8,685±295[6] K |
| Metallicity [Fe/H] | −0.16[3] dex |
| Rotation | 0.79 days[8] |
| 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[9] | |
| 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.[10] The star displays an infrared excess, suggesting the presence of a circumstellar disk of orbiting dust.[11]
Epsilon Gruis is suspected of having a moderately active[12] close companion,[13] 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.[12]