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HK Aquarii

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Star in the constellation Aquarius
HK Aquarii

A visual band light curve for HK Aquarii, adapted from Young et al. (1990)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 23 08 19.55110
Declination 15° 24′ 35.7682″
Apparent magnitude (V) 10.99±0.02
10.72 - 10.94
Characteristics
Evolutionary stage Main sequence
Spectral type M0Ve
U−B color index +1.118
B−V color index +1.31
Variable type BY Dra + UV Cet
Astrometry
Radial velocity (Rv)+2.7±1.6 km/s
Proper motion (μ) RA: 106.955 mas/yr
Dec.: −18.738 mas/yr
Parallax (π)40.1410 ± 0.0436 mas
Distance81.25 ± 0.09 ly
(24.91 ± 0.03 pc)
Absolute magnitude (MV)+9.13
Details
Mass0.57±0.07 M☉
Radius0.53±0.04 R☉
Luminosity0.05±0.01 L☉
Temperature3,800±76 K
Metallicity 0.27±0.12 dex
Rotation0.4307 d
Rotational velocity (v sin i)69.0±0.1 km/s km/s
Age30–40 Myr
Other designations
HK Aqr, NSV 14434, BD−16°6218, GJ 890, HIP 114252
Database references
SIMBADdata

HK Aquarii is a single variable star in the equatorial constellation of Aquarius. It is invisible to the naked eye, having an average apparent visual magnitude that fluctuates around 10.99. The star is located at a distance of 81 light years from the Sun based on parallax. The radial velocity is poorly constrained but it appears to be drifting further away at a rate of ~2 km/s.

In 1983, Arthur Young et al. discovered that the star, called GLS 890 at that time, is a variable star. They also noted its very rapid rotation. It was given its variable star designation, HK Aquarii, in 1987.

This is a small red dwarf star; an M-type main-sequence star with a stellar classification of M0Ve, where the 'e' indicates emission lines in the spectrum. It has 57% of the mass of the Sun and has 53% of the Sun's girth. The star is spinning with a projected rotational velocity of 69 km/s and has a rotation period of just 10.34 hours. Based on the abundance of iron in the atmosphere, it has a high metallicity; what astronomers term the abundances of elements with a higher atomic number than helium. The star is radiating around 5% of the luminosity of the Sun from its photosphere at an effective temperature of 3,800 K.

HK Aquarii is classified as a BY Draconis variable and has been observed ranging in brightness from visual magnitude 10.72 down to 10.94. This star is 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. Star spots have been reported at a variety of latitudes, but not at the poles. Flaring activity was reported in 1987, and a steady X-ray emission has been detected. 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. (A 2016 study instead suggests it is a member of the Octans association.)

The signature of prominences has been detected in the star's atmosphere. These display evidence of periodic oscillations and can reach altitudes greater than two-third's of the star's radius. The prominences can obtain a higher mass and volume compared to similar features on the Sun.

References

  1. Young, Arthur; Skumanich, Andrew; MacGregor, Keith B.; Temple, Scott (February 1990). "High-Latitude SPOT and Plage Activity on the Rapidly Rotating M Dwarf Star Gliese 890". The Astrophysical Journal. 349: 608–619. Bibcode:1990ApJ...349..608Y. doi:10.1086/168347. Retrieved 17 October 2021.
  2. ^ 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.
  3. ^ Gaidos, E.; et al. (September 2014). "Trumpeting M dwarfs with CONCH-SHELL: a catalogue of nearby cool host-stars for habitable exoplanets and life". Monthly Notices of the Royal Astronomical Society. 443 (3): 2561–2578. arXiv:1406.7353. Bibcode:2014MNRAS.443.2561G. doi:10.1093/mnras/stu1313.
  4. ^ Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  5. ^ Torres, C. A. O.; et al. (2015). "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. S2CID 16080025.
  6. ^ Koen, C.; et al. (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.
  7. ^ 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
  8. ^ Strassmeier, Klaus G. (September 2009). "Starspots". The Astronomy and Astrophysics Review. 17 (3): 251–308. Bibcode:2009A&ARv..17..251S. doi:10.1007/s00159-009-0020-6.
  9. ^ Barnes, J. R.; Collier, Cameron, A. (September 2001). "Starspot patterns on the M dwarfs HK Aqr and RE 1816 +541". Monthly Notices of the Royal Astronomical Society. 326 (3): 950–958. Bibcode:2001MNRAS.326..950B. doi:10.1046/j.1365-8711.2001.04649.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ Elliott, P.; et al. (May 2016). "Search for associations containing young stars (SACY). VII. New stellar and substellar candidate members in the young associations". Astronomy & Astrophysics. 590: 28. arXiv:1604.03550. Bibcode:2016A&A...590A..13E. doi:10.1051/0004-6361/201628253. S2CID 53138126. A13.
  11. Young, A.; Skumanich, A.; MacGregor, K.; Temple, S. (September 1984). "The Extremely Rapidly Rotating M-Dwarf Star Gliese 890". Bulletin of the American Astronomical Society. 16: 1014. Bibcode:1984BAAS...16.1014Y. Retrieved 19 November 2024.
  12. Kholopov, P. N.; Samus, N. N.; Kazarovets, E. V.; Kireeva, N. N. (August 1987). "The 68th Name-List of Variable Stars" (PDF). Information Bulletin on Variable Stars. 3058: 1–30. Bibcode:1987IBVS.3058....1K. Retrieved 19 November 2024.
  13. ^ Crosswell, Ken (1992). A Star that Breaks all the Rules. Kalmbach Books. pp. 54–59. {{cite book}}: |work= ignored (help)
  14. Barnes, J. R.; et al. (August 2004). "Differential rotation and star-spot evolution on HK Aqr in 2001 and 2002". Monthly Notices of the Royal Astronomical Society. 352 (2): 589–599. Bibcode:2004MNRAS.352..589B. doi:10.1111/j.1365-2966.2004.07949.x.
  15. Leitzinger, M.; et al. (November 2016). "Indications of stellar prominence oscillations on fast rotating stars: the cases of HK Aqr and PZ Tel". Monthly Notices of the Royal Astronomical Society. 463 (1): 965–979. arXiv:1608.00453. Bibcode:2016MNRAS.463..965L. doi:10.1093/mnras/stw1922.
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