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]

References

1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
2. Høg, E.; et al. (2000), "The Tycho-2 catalogue of the 2.5 million brightest stars", Astronomy and Astrophysics, 355: L27, Bibcode:2000A&A...355L..27H, doi:10.1888/0333750888/2862, ISBN 978-0333750889.
3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992.
4. Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169.
5. Ammler-von Eiff, Matthias; Reiners, Ansgar (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724, S2CID 53666672.
6. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
7. "eps Gru". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-09-22.
8. Belle, G. T. (2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.
9. Ertel, S.; et al. (October 2014), "A near-infrared interferometric survey of debris-disk stars. IV. An unbiased sample of 92 southern stars observed in H band with VLTI/PIONIER", Astronomy & Astrophysics, 570: 20, arXiv:1409.6143, Bibcode:2014A&A...570A.128E, doi:10.1051/0004-6361/201424438, S2CID 9594917, A128.
10. Schröder, C.; et al. (June 2008), "Magnetic fields in A-type stars associated with X-ray emission", Astronomy and Astrophysics, 484 (2): 479–486, Bibcode:2008A&A...484..479S, doi:10.1051/0004-6361:20078963.
11. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.