HK Aquarii

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Gliese 890 / HK Aquarii
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension  23h 08m 19.551s [1]
Declination 15° 24′ 35.77″[1]
Apparent magnitude (V) 10.72 - 10.94[2]
Evolutionary stage Red dwarf
Spectral type M0Ve[3]
U−B color index +1.118[4]
B−V color index +1.41[4]
Variable type BY Dra[5]
Proper motion (μ) RA: 106.955[1] mas/yr
Dec.: -18.738[1] mas/yr
Parallax (π)40.1410 ± 0.0436[1] mas
Distance81.25 ± 0.09 ly
(24.91 ± 0.03 pc)
Absolute magnitude (MV)+9.13[4]
Mass0.5[5] M
Radius0.6[5] R
Other designations
BD−16 6218, HIP 114252
Database references

HK Aquarii (Gliese 890) is a variable star--technically a BY Draconis variable--noteworthy for being unusually active for an isolated red dwarf; it rotates rapidly, generating a strong magnetic field that creates large starspots and powerful flares. These are characteristic of very young stars; although it is not close to any youthful open cluster, it is a possible ejected member of the Pleiades.[5]


  1. ^ a b c d e 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. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published In: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
  3. ^ Torres, C. A. O.; Quast, G. R.; Da Silva, L.; de la Reza, R.; Melo, C. H. F.; Sterzik, M. (2006). "Search for associations containing young stars (SACY). I. Sample and searching method". Astronomy and Astrophysics. 460 (3): 695. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602.
  4. ^ a b c Koen, C.; Kilkenny, D.; Van Wyk, F.; Marang, F. (2010). "UBV(RI)C JHK observations of Hipparcos-selected nearby stars". Monthly Notices of the Royal Astronomical Society. 403 (4): 1949. Bibcode:2010MNRAS.403.1949K. doi:10.1111/j.1365-2966.2009.16182.x.
  5. ^ a b c d Crosswell, Ken. "A Star that Breaks all the Rules." The New Cosmos. Astronomy Magazine, Kalmbach Books, 1992, pp. 54-59.