Eta Gruis

Eta Gruis, Latinized from η Gruis, is a solitary[7] star in the southern constellation of Grus. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.85.[2] Based upon an annual parallax shift of 7.1 mas as seen from the Earth,[8] the system is located about 460 light years from the Sun. The star is drifting further away with a radial velocity of +28 km/s.[4]

Eta Gruis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Grus
Right ascension 22h 45m 37.88285s[1]
Declination −53° 30′ 00.4405″[1]
Apparent magnitude (V) 4.85[2]
Characteristics
Spectral type K2 III CNIV[3]
U−B color index +1.17[2]
B−V color index +1.18[2]
Astrometry
Radial velocity (Rv)+27.8±2.8[4] km/s
Proper motion (μ) RA: +30.207[1] mas/yr
Dec.: +17.921[1] mas/yr
Parallax (π)7.1001 ± 0.1924[1] mas
Distance460 ± 10 ly
(141 ± 4 pc)
Absolute magnitude (MV)−0.68[5]
Details
Radius31.38+0.92
−1.04[1] R☉
Luminosity338.5±10.5[1] L☉
Temperature4,420+75
−64[1] K
Other designations
η Gru, CPD−54° 10123, FK5 3821, HD 215369, HIP 112374, HR 8655, SAO 247570, WDS J22456-5330A[6]
Database references
SIMBADdata

This object is an evolved K-type giant star with a stellar classification of K2 III CNIV,[3] where the suffix notation indicates this is an intermediate CN star. It is a periodic microvariable with an amplitude of 0.0055 magnitude and a frequency of 0.36118 cycles per day.[9] With the supply of hydrogen exhausted at its core, the star has expanded and cooled, now having 31[1] times the Sun's girth. It is radiating 338.5[1] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,420 K.[1]

Eta Gruis has a magnitude 11.5 visual companion located at an angular separation of 25.6″ along a position angle of 187°, as of 2012.[10]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J.
  3. Houk, Nancy; Cowley, A. P. (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H.
  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.
  5. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  6. "eta Gru". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-06-28.
  7. 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.
  8. 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.
  9. Koen, Chris; Eyer, Laurent (2002), "New periodic variables from the Hipparcos epoch photometry", Monthly Notices of the Royal Astronomical Society, 331: 45, arXiv:astro-ph/0112194, Bibcode:2002MNRAS.331...45K, doi:10.1046/j.1365-8711.2002.05150.x.
  10. Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
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