Alcyone (star)

Alcyone (star)
Image of the Pleiades star cluster
Alcyone in the Pleiades cluster (circled)
Observation data
Epoch J2000      Equinox ICRS
Constellation Taurus
Right ascension 03h 47m 29.077s
Declination +24° 06′ 18.49″
Apparent magnitude (V) 2.87
Characteristics
Evolutionary stage subgiant
Spectral type B7IIIe
U−B color index −0.34
B−V color index −0.09
Astrometry
Radial velocity (Rv)5.40 km/s
Proper motion (μ) RA: 19.34±0.39 mas/yr
Dec.: −43.67±0.33 mas/yr
Parallax (π)8.09±0.42 mas
Distance136 pc
Absolute magnitude (MV)−2.62
Details
Mass5.9 – 6.1 M☉
Radius10.56 (equatorial)
8.0 (polar) R☉
Luminosity1,750±50 L☉
Surface gravity (log g)3.047 cgs
Temperature12,258 K
Rotational velocity (v sin i)149 km/s
Age70 Myr
Other designations
η Tau, 25 Tau, HR 1165, HD 23630, BD+23 541, FK5 139, HIP 17702, SAO 76199, GC 4541, BDS 1875, CCDM 03474+2407
Database references
SIMBADdata

Alcyone /ælˈsaɪəniː/, is a blue-white giant star and the brightest star in the Pleiades open cluster. At apparent magnitude 2.87, it is also the third-brightest star in the constellation Taurus. The star has the Bayer designation Eta Tauri, Latinized from η Tauri and abbreviated Eta Tau or η Tau. It is about 440 light-years distant.

Nomenclature

Eta Tauri is the star's Bayer designation. The name Alcyone originates in Greek mythology; she is one of the seven daughters of Atlas and Pleione known as the Pleiades. In 2016, the International Astronomical Union (IAU) organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Alcyone for this star. It is now so entered in the IAU Catalog of Star Names.

In Chinese, 昴宿 (Mǎo Xiù), meaning Hairy Head, refers to an asterism consisting Alcyone, Electra, Taygeta, Asterope, Maia, Merope, and Atlas. Consequently, the Chinese name for Alcyone itself is 昴宿六 (Mǎo Xiù liù), "the Sixth Star of Hairy Head".

Physical properties

Alcyone is a blue-white B-type giant, similar to the other bright B-type stars in the Pleiades cluster. With an apparent magnitude of +2.87 and absolute magnitude of −2.39, it is the brightest and most luminous star in the Pleiades. The spectral type of B7IIIe indicates that emission lines are present in its spectrum. Like many Be stars, Alcyone has created a gaseous disk flung into orbit around the star from its equator.

Alcyone has a high rotational velocity, which causes it to have an ellipsoidal shape. Its effective radius is almost ten times that of the Sun, but the actual radius is lesser at poles and greater at the equator. Its effective temperature is 12,258 K, with the actual temperature being greater at the poles and lesser at the equator. Its bolometric luminosity is 1,750 times solar. The rapid rotation causes Alcyone to be an oblate shape, with the equatorial radius being 10.56 R☉ and the polar radius to be 8.0 R☉.

The age of the Pleiades is typically calculated to be around 130 million years, but Alcyone itself appears to be younger, less than 100 million years. Alcyone may be a blue straggler or models may not be deriving an accurate age for stars of this type.

Variability

A light curve for Alcyone, adapted from White et al. (2017)

Alcyone has long been suspected to vary in brightness, and a 2017 study using data from the Kepler Space Telescope found definite periodic variations with amplitudes up to 0.001 magnitudes. This is considered undetectable by ground-based observations. The strongest period of 2.3 days is thought to be the rotation period of the star, with an uneven surface causing slight brightness changes, but there are also more rapid pulsations and Alcyone has been classified as both a rotational variable and a slowly pulsating B-type star.

As of 2025, Alcyone has not been formally listed as a variable star in the General Catalogue of Variable Stars.

Companions

The Catalog of Components of Double and Multiple Stars lists three companions: B is 24 Tauri, a magnitude 6.28 A0 main-sequence star 117" away; C is V647 Tauri, a δ Sct variable star; and D is a magnitude 9.15 F3 main-sequence star. V647 Tau varies from magnitude +8.25 to +8.30 over 1.13 hours.

The Washington Double Star Catalog lists a further four companions, all fainter than 11th magnitude, and also describes component D as itself double with two nearly equal components separated by 0.30".

Some previous lunar occultation studies found evidence of sub-arcsecond companions, but more recently, a 2021 interferometric study concluded that Alcyone is a single star system.

See also

References

  1. 1 2 3 4 5 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Vizier catalog entry
  2. 1 2 3 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. ↑ Fritzewski, D. J.; Kemp, A.; Li, G.; Aerts, C. (2026). "Probing stellar rotation in the Pleiades with gravity-mode pulsators". Astronomy & Astrophysics. 706: A131. arXiv:2512.09395. doi:10.1051/0004-6361/202557416.
  4. ↑ Jaschek, C.; Jaschek, M. (1992). "A southern be star survey : Spectra and envelope radii". Astronomy and Astrophysics Supplement Series. 95: 535. Bibcode:1992A&AS...95..535J.
  5. ↑ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 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.
  6. ↑ Melis, Carl; Reid, Mark J.; Mioduszewski, Amy J.; Stauffer, John R.; et al. (29 August 2014). "A VLBI resolution of the Pleiades distance controversy". Science. 345 (6200): 1029–1032. arXiv:1408.6544. Bibcode:2014Sci...345.1029M. doi:10.1126/science.1256101. PMID 25170147. S2CID 34750246.
  7. ↑ Zhang, P.; Liu, C. Q.; Chen, P. S. (2006). "Absolute Magnitudes of Be Stars Based on Hipparcos Parallaxes". Astrophysics and Space Science. 306 (3): 113. Bibcode:2006Ap&SS.306..113Z. doi:10.1007/s10509-006-9173-1. S2CID 122897957.
  8. ↑ Zorec, J.; Frémat, Y.; Cidale, L. (2005). "On the evolutionary status of Be stars. I. Field Be stars near the Sun". Astronomy and Astrophysics. 441 (1): 235–248. arXiv:astro-ph/0509119. Bibcode:2005A&A...441..235Z. doi:10.1051/0004-6361:20053051. S2CID 17592657.
  9. 1 2 3 Klement, R.; Carciofi, A. C.; Rivinius, T.; Matthews, L. D.; Vieira, R. G.; Ignace, R.; Bjorkman, J. E.; Mota, B. C.; Faes, D. M.; Bratcher, A. D.; Curé, M.; Štefl, S. (2017). "Revealing the structure of the outer disks of be stars". Astronomy and Astrophysics. 601: A74. arXiv:1703.07321. Bibcode:2017A&A...601A..74K. doi:10.1051/0004-6361/201629932. S2CID 56439879.
  10. 1 2 3 4 Touhami, Y.; Gies, D. R.; Schaefer, G. H.; McAlister, H. A.; Ridgway, S. T.; Richardson, N. D.; Matson, R.; Grundstrom, E. D.; Ten Brummelaar, T. A.; Goldfinger, P. J.; Sturmann, L.; Sturmann, J.; Turner, N. H.; Farrington, C. (2013). "A CHARA Array Survey of Circumstellar Disks around Nearby Be-type Stars". The Astrophysical Journal. 768 (2): 128. arXiv:1302.6135. Bibcode:2013ApJ...768..128T. doi:10.1088/0004-637X/768/2/128. S2CID 9488327.
  11. 1 2 Brandt, Timothy D.; Huang, Chelsea X. (2015). "Bayesian Ages for Early-type Stars from Isochrones Including Rotation, and a Possible Old Age for the Hyades". The Astrophysical Journal. 807 (1): 58. arXiv:1501.04404. Bibcode:2015ApJ...807...58B. doi:10.1088/0004-637X/807/1/58. S2CID 119045213.
  12. ↑ "Alcyone". Merriam-Webster.com Dictionary. Merriam-Webster. OCLC 1032680871.
  13. ↑ "IAU Working Group on Star Names (WGSN)". Archived from the original on 10 June 2016. Retrieved 22 May 2016.
  14. ↑ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  15. ↑ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  16. ↑ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  17. ↑ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  18. 1 2 White, T. R.; et al. (2017). "Beyond the Kepler/K2 bright limit: Variability in the seven brightest members of the Pleiades". Monthly Notices of the Royal Astronomical Society. 471 (3): 2882–2901. arXiv:1708.07462. Bibcode:2017MNRAS.471.2882W. doi:10.1093/mnras/stx1050. S2CID 119221178.
  19. ↑ Hartkopf, W. I.; McAlister, H. A. (1984). "Binary stars unresolved by speckle interferometry. III". Publications of the Astronomical Society of the Pacific. 96: 105. Bibcode:1984PASP...96..105H. doi:10.1086/131309.
  20. ↑ "Alcyone". International Variable Star Index. Retrieved 2025-05-08.
  21. 1 2 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.
  22. ↑ Gebran, M.; Monier, R. (2008). "Chemical composition of a and F dwarfs members of the Pleiades open cluster". Astronomy and Astrophysics. 483 (2): 567. arXiv:0802.3148. Bibcode:2008A&A...483..567G. doi:10.1051/0004-6361:20079271. S2CID 18923359.
  23. ↑ Dommanget, J.; Nys, O. (1994). "Catalogue of the Components of Double and Multiple stars (CCDM). First edition". Obs. R. Belg., Commun., Sér. A. 115. Bibcode:1994CoORB.115.....D.
  24. ↑ Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  25. ↑ Hutter, D. J.; Tycner, C.; Zavala, R. T.; Benson, J. A.; Hummel, C. A.; Zirm, H. (2021-12-01). "Surveying the Bright Stars by Optical Interferometry III: A Magnitude-Limited Multiplicity Survey of Classical Be-Stars". The Astrophysical Journal Supplement Series. 257 (2): 69. arXiv:2109.06839. Bibcode:2021ApJS..257...69H. doi:10.3847/1538-4365/ac23cb. ISSN 0067-0049. S2CID 237503492.