LQ Hydrae

LQ Hydrae is a single[13] variable star in the equatorial constellation of Hydra. It is sometimes identified as Gl 355 from the Gliese Catalogue; LQ Hydrae is the variable star designation, which is abbreviated LQ Hya.[14] The brightness of the star ranges from an apparent visual magnitude of 7.79 down to 7.86,[5] which is too faint to be readily visible to the naked eye. Based on parallax measurements, this star is located at a distance of 59.6 light years from the Sun. It is drifting further away with a radial velocity of 7.6 km/s.[7]

LQ Hydrae

A visual band light curve for LQ Hydrae. The main plot (adapted from Berdyugina et al.[1]) shows the long-term variation, and the inset plot (adapted from Kiraga[2]) shows the periodic variation.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hydra
Right ascension 09h 32m 25.568s[3]
Declination −11° 11′ 04.69″[3]
Apparent magnitude (V) 7.82[4] (7.79 to 7.86)[5]
Characteristics
Evolutionary stage Main sequence
Spectral type K1Vp[6]
B−V color index 0.933±0.021[4]
Variable type BY Dra[5]
Astrometry
Radial velocity (Rv)7.58±0.27[7] km/s
Proper motion (μ) RA: −248.040 mas/yr[3]
Dec.: 34.277 mas/yr[3]
Parallax (π)54.7362 ± 0.0244 mas[3]
Distance59.59 ± 0.03 ly
(18.269 ± 0.008 pc)
Absolute magnitude (MV)6.47[6]
Details
Mass0.81[8] M☉
Radius1.0[9] R☉
Luminosity0.282±0.001[3] L☉
Surface gravity (log g)4.57[8] cgs
Temperature4,812±39[8] K
Metallicity [Fe/H]0.32[8] dex
Rotation1.601[9] d
Rotational velocity (v sin i)25±2[10] km/s
AgeUnder 75[11] Myr
Other designations
LQ Hya, BD−10 2857, GC 13168, GJ 355, HD 82558, HIP 46816, SAO 155272, LTT 3510[12]
Database references
SIMBADdata

During a 1981 survey of southern stars, W. P. Bidelman found the H and K lines of ionized calcium for LQ Hya were filled in with emission. (W. D. Heintz independently made the same observation.) In 1986, F. C. Fekel and associates determined this is a young, rapidly rotating BY Draconis-type variable.[13][15] A decade of photometry was used to determine a rotation period of 1.601136±0.000013 days (1 day, 14 hours, and 24 minutes) The star spots on the surface showed significant evolution over time scales of a few months. Variations in rotational modulation of surface activity suggested the star is undergoing differential rotation.[10]

The high lithium abundance and rapid rotation of this star indicate it is a zero age main sequence star, or possibly even a pre-main sequence star.[14] A strong flare event was observed on December 22, 1993, with an estimated energy release of ~5.7×1033 erg.[11] Additional flares were detected thereafter, with ROSAT X-ray data from 1992 showing a strong flare during that time period.[14] Observations from December 2000 and 2001 showed that the magnetic field of the star is dramatically changing its topology on a time frame of a year or less.[16]

The stellar classification of LQ Hya is K1Vp,[6] indicating it is a K-type main-sequence star with some peculiar features in the spectrum. In some respects it is considered an analog of a young Sun around the age of 60 million years.[1] It shows strong emission of ultraviolet and has been detected in the X-ray band, showing an X-ray emission of 8.8×1029 erg/s and indicating high chromospheric activity levels.[14] The star shows dual magnetic activity cycles with period of 6.8 and 11.4 years,[14] which are somewhat comparable to the solar cycle in the Sun.

References
  1. Berdyugina, S. V.; et al. (November 2002), "Magnetic activity in the young solar analog LQ Hydrae. I. Active longitudes and cycles", Astronomy and Astrophysics, 394 (2): 505–515, Bibcode:2002A&A...394..505B, doi:10.1051/0004-6361:20021179.
  2. Kiraga, M. (March 2012). "ASAS Photometry of ROSAT Sources. I. Periodic Variable Stars Coincident with Bright Sources from the ROSAT All Sky Survey" (PDF). Acta Astronomica. 62 (1): 67–95. arXiv:1204.3825. Bibcode:2012AcA....62...67K. Retrieved 23 June 2022.
  3. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  4. 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, S2CID 119257644.
  5. Samus', N. N; et al. (2017), "General catalogue of variable stars", Astronomy Reports, GCVS 5.1, 61 (1): 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  6. Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
  7. Halbwachs, J. -L.; et al. (2018), "Multiplicity among solar-type stars. IV. The CORAVEL radial velocities and the spectroscopic orbits of nearby K dwarfs", Astronomy and Astrophysics, 619: A81, arXiv:1808.04605, Bibcode:2018A&A...619A..81H, doi:10.1051/0004-6361/201833377, S2CID 119437322.
  8. Luck, R. Earle (March 2018), "Abundances in the Local Region. III. Southern F, G, and K Dwarfs", The Astronomical Journal, 155 (3): 31, Bibcode:2018AJ....155..111L, doi:10.3847/1538-3881/aaa9b5, S2CID 125765376, 111.
  9. 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.
  10. Jetsu, L. (September 1993), "A decade of photometry of LQ Hydrae", Astronomy and Astrophysics, 276: 345–352, Bibcode:1993A&A...276..345J.
  11. Montes, D.; et al. (May 1999), "Optical and ultraviolet observations of a strong flare in the young, single K2 dwarf LQ Hya", Monthly Notices of the Royal Astronomical Society, 305 (1): 45–60, arXiv:astro-ph/9811452, Bibcode:1999MNRAS.305...45M, doi:10.1046/j.1365-8711.1999.02373.x, S2CID 10033733.
  12. "LQ Hya", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2022-02-23.
  13. Fekel, F. C.; et al. (November 1986), "Chromospherically active stars. II. HD 82558, a young single BY Draconis variable", Astronomical Journal, 92: 1150–1154, Bibcode:1986AJ.....92.1150F, doi:10.1086/114246.
  14. Covino, S.; et al. (June 2001), "Quiescent and flare analysis for the chromospherically active star Gl 355 (LQ Hya)", Astronomy and Astrophysics, 371 (3): 973–985, arXiv:astro-ph/0103473, Bibcode:2001A&A...371..973C, doi:10.1051/0004-6361:20010454, S2CID 119518367.
  15. Fekel, F. C.; et al. (February 1986), "A Survey of Chromospherically Active Stars", Astrophysical Journal Supplement, 60: 551, Bibcode:1986ApJS...60..551F, doi:10.1086/191097.
  16. McIvor, T.; et al. (December 2004), "The changing corona of LQ Hya", Monthly Notices of the Royal Astronomical Society, 355 (4): 1066–1072, Bibcode:2004MNRAS.355.1066M, doi:10.1111/j.1365-2966.2004.08391.x, S2CID 120518212.

Further reading
  • Cole-Kodikara, Elizabeth M.; et al. (September 2019), "Spot evolution on LQ Hya from 2006-2017: temperature maps based on SOFIN and FIES data", Astronomy & Astrophysics, 629: 9, arXiv:1904.08713, Bibcode:2019A&A...629A.120C, doi:10.1051/0004-6361/201935729, S2CID 121348666, A120.
  • Cole, E. M.; et al. (September 2015), "Doppler imaging of LQ Hydrae for 1998-2002", Astronomy & Astrophysics, 581: 9, arXiv:1504.03673, Bibcode:2015A&A...581A..69C, doi:10.1051/0004-6361/201425440, S2CID 118155166, A69.
  • Zhang, Liyun; et al. (October 2014), "Chromospheric activity on late-type star LQ Hya", New Astronomy, 32: 1–5, Bibcode:2014NewA...32....1Z, doi:10.1016/j.newast.2014.02.010.
  • Cao, Dong-tao; et al. (February 2014), "Chromospheric Activity and Rotational Modulation on the Young, Single K2 Dwarf LQ Hya", The Astronomical Journal, 147 (2): 10, Bibcode:2014AJ....147...38C, doi:10.1088/0004-6256/147/2/38, S2CID 120310890, 38.
  • Kõvári, Zs.; Weber, M. (June 2004), Forgács-Dajka, E.; Petrovay, K.; Erdélyi, R. (eds.), "Differential rotation of LQ Hya and IL Hya from Doppler imaging", Proceedings of the British-Hungarian N+N Workshop for Young Researchers On Computer processing and use of satellite data in astronomy and astrophysics and 3rd Workshop of Young Researchers in Astronomy & Astrophysics; Hungary, 3-7 February 2004, Publications of the Astronomy Department of the Eötvös University (PADEU), vol. 14, pp. 221–232, Bibcode:2004PADEU..14..221K.
  • Livshits, M. A.; Alekseev, I. Yu.; Katsova, M. M. (July 2003), "Butterfly Diagram for Starspots on LQ Hya", Astronomy Reports, 47 (7): 562–572, Bibcode:2003ARep...47..562L, doi:10.1134/1.1592835, S2CID 122361382.
  • Alekseev, I. Yu.; Kozlova, O. V. (January 2003), "Spots and Active Regions on Emission Stars. III. LQ Hya", Astrophysics (English Translation of Astrofizika), 46 (1): 28–45, Bibcode:2003Ap.....46...28A, doi:10.1023/A:1022959419060, S2CID 116908588.
  • Donati, J. -F. (January 1999), "Magnetic cycles of HR 1099 and LQ Hydrae", Monthly Notices of the Royal Astronomical Society, 302 (3): 457–481, Bibcode:1999MNRAS.302..457D, doi:10.1046/j.1365-8711.1999.02096.x.
  • Saar, S. H.; et al. (1994), Caillault, J.-P. (ed.), "Multiple Epoch Magnetic Surface Images of LQ Hya", The Eighth Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Astronomical Society of the Pacific Conference Series, vol. 64, pp. 661–663, Bibcode:1994ASPC...64..661S.
  • Strassmeier, K. G.; et al. (February 1993), "Surface features of the lower atmosphere of HD 82558 (=LQ Hydrae)", Astronomy and Astrophysics, 268: 671–684, Bibcode:1993A&A...268..671S.
  • Saar, S. H.; et al. (1992), Giampapa, M. S.; Bookbinder, J. A. (eds.), "Magnetic Surface Images of the BY DRA Star HD 82558", The Seventh Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Astronomical Society of the Pacific Conference Series, vol. 26, pp. 255–258, Bibcode:1992ASPC...26..255S.


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