HK Aquarii

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]
Characteristics
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]
Astrometry
Proper motion (μ)	RA: 106.955[1] mas/yr ; Dec.: -18.738[1] mas/yr
Parallax (π)	40.1410 ± 0.0436[1] mas
Distance	81.25 ± 0.09 ly ; (24.91 ± 0.03 pc)
Absolute magnitude (MV)	+9.13[4]
Details
Mass	0.5[5] M☉
Radius	0.6[5] R☉
Other designations
	BD−16 6218, HIP 114252
Database references
SIMBAD	data

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]

References

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.
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.
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. arXiv:1505.07837. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602.
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.
Crosswell, Ken. "A Star that Breaks all the Rules." The New Cosmos. Astronomy Magazine, Kalmbach Books, 1992, pp. 54-59.

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[dr2-1] 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.

[gcvs-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.

[sacy-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. arXiv:1505.07837. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602.

[koen-4] 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.

[crosswell-5] Crosswell, Ken. "A Star that Breaks all the Rules." The New Cosmos. Astronomy Magazine, Kalmbach Books, 1992, pp. 54-59.