EQ Tauri

A visual band light curve for EQ Tauri, plotted from ASAS-SN[1] data
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Right ascension 03h 48m 13.436s[2]
Declination +22° 18′ 50.92″[2]
Apparent magnitude (V) 10.5 (-11.03)[3]
Characteristics
Spectral type G2[4]
Variable type W UMa[3]
Astrometry
Radial velocity (Rv)71.95±1.22[5] km/s
Proper motion (μ) RA: +69.758 mas/yr[2]
Dec.: −30.628 mas/yr[2]
Parallax (π)4.4694 ± 0.0171 mas[2]
Distance730 ± 3 ly
(223.7 ± 0.9 pc)
Orbit[6]
Period (P)0.341348 d
Semi-major axis (a)2.48±0.03 R☉[7]
Eccentricity (e)0.00
Periastron epoch (T)2,451,183.9 HJD
Semi-amplitude (K1)
(primary)		112.41±1.43 km/s
Semi-amplitude (K2)
(secondary)		254.38±2.42 km/s
Details
Primary
Mass1.22±0.04[7] M☉
Radius1.14±0.01[7] R☉
Luminosity1.32±0.03[7] L☉
Temperature5,800±100[7] K
Secondary
Mass0.54±0.02[7] M☉
Radius0.79±0.01[7] R☉
Luminosity0.63±0.02[7] L☉
Other designations
EQ Tau, TIC 440686937, GSC 01260-00909, 2MASS J03481342+2218509, HV 6189[8]
Database references
SIMBADdata

EQ Tauri is a triple star system in the equatorial constellation of Taurus that includes a contact eclipsing binary. The system is too faint to be viewed with the naked eye, having a baseline apparent visual magnitude of 10.5.[3] During the primary eclipse, the brightness of the system drops to magnitude 11.03, then to 10.97 during the secondary minimum.[3] The secondary eclipse is total.[7] Based on parallax measurements, it is located at a distance of approximately 730 light years from the Sun.[2]

The star HV 6189 was identified as a short-period variable by H. Shapley and E. M. Hughes in 1940,[9] then was more closely studied by Soviet astronomer V. P. Tsesevich in 1954.[6] It was determined to be a W UMa-type variable and was noted for being located in the region of the Pleiades open cluster.[10] An analysis of data from Tsesevich and subsequent observations by B. S. Whitney in 1972 suggested that the period is variable. His observations from Konkoly Observatory showed a period of 8.19 h.[11] W. R. Benbow and R. L. Mutel built a light curve of the eclipsing variable in 1995 that displayed evidence of an active region on the stellar surface.[12] Orbital period changes continued to be observed, and in 2002 T. Pribulla and M. Vanko suggested it is caused by a third body in the system. They modeled it as a low mass red dwarf with an orbital period of 50.2 years.[13]

This is a shallow contact binary system,[7] belonging to sub-type A of the W Ursae Majoris class.[3] It has an orbital period of 8.1924 hours[6] and a semimajor axis of 2.48 times the radius of the Sun. The orbit shows a cyclical change with a period of 22.7 years and an amplitude of 0.0058 days. A transit-like event was observed in 2010.[7] The more massive component is a solar-type star with a deep convection zone that appears magnetically active with a significant coverage of star spots.[4]

References

  1. ^ "ASAS-SN Variable Stars Database". ASAS-SN Variable Stars Database. ASAS-SN. Retrieved 6 January 2022.
  2. ^ a b c d e 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.
  3. ^ a b c d e 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.
  4. ^ a b Yuan, Jinzhao; Qian, Shengbang (October 2007), "Variation of the period and light curves of the solar-type contact binary EQ Tauri", Monthly Notices of the Royal Astronomical Society, 381 (2): 602–610, Bibcode:2007MNRAS.381..602Y, doi:10.1111/j.1365-2966.2007.11926.x.
  5. ^ Bilir, S.; et al. (2005), "Kinematics of W Ursae Majoris type binaries and evidence of the two types of formation", Monthly Notices of the Royal Astronomical Society, 357 (2): 497–517, arXiv:astro-ph/0411291, Bibcode:2005MNRAS.357..497B, doi:10.1111/j.1365-2966.2005.08609.x, S2CID 16274339.
  6. ^ a b c Rucinski, Slavek M.; et al. (October 2001), "Radial Velocity Studies of Close Binary Stars. V.", The Astronomical Journal, 122 (4): 1974–1980, arXiv:astro-ph/0106160, Bibcode:2001AJ....122.1974R, doi:10.1086/323106.
  7. ^ a b c d e f g h i j k Li, K.; et al. (May 2014), "The Triple Binary Star EQ Tau with an Active Component", The Astronomical Journal, 147 (5): 8, Bibcode:2014AJ....147...98L, doi:10.1088/0004-6256/147/5/98, S2CID 123566937, 98.
  8. ^ "EQ Tau", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2022-03-13.
  9. ^ Shapley, Harlow; Hughes, Emily M. (1940), "Variable stars in high galactic latitudes", Annals of the Astronomical Observatory of Harvard College, 90 (4): 163–175, Bibcode:1940AnHar..90..163S.
  10. ^ Artiukhina, N. M. (1961), "Proper Motions of three W UMa Type Stars in the Pleiades Region", Peremennye Zvezdy (in Russian), 13: 366, Bibcode:1961PZ.....13..366A.
  11. ^ Whitney, B. S. (February 1972), "The Period of EQ Tauri", Information Bulletin on Variable Stars, 633 (1): 1, Bibcode:1972IBVS..633....1W.
  12. ^ Benbow, W. R.; Mutel, R. L. (May 1995), "Eclipse Observations of EQ Tau", Information Bulletin on Variable Stars, 4187 (1): 1, Bibcode:1995IBVS.4187....1B.
  13. ^ Pribulla, T.; Vanko, M. (April 2002), "Photoelectric photometry of eclipsing contact binaries: U Peg, YY CrB, OU Ser and EQ Tau", Contributions of the Astronomical Observatory Skalnate Pleso, 32 (1): 79–98, Bibcode:2002CoSka..32...79P.

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