21 Tauri


21 Tauri
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
Right ascension 03h 45m 54.47676s[1]
Declination +24° 33′ 16.2418″[1]
Apparent magnitude (V) 5.76[2]
Evolutionary stage main sequence[2]
Spectral type B8 V[3]
B−V color index +0.04[2]
Radial velocity (Rv)+6.0±0.6[4] km/s
Proper motion (μ) RA: +20.025[5] mas/yr
Dec.: −45.949[5] mas/yr
Parallax (π)7.5658 ± 0.1321[1] mas
Distance431 ± 8 ly
(132 ± 2 pc)
Absolute magnitude (MV)+0.34[6]
Mass2.93±0.07[2] M
[2] L
Surface gravity (log g)4.250±0.113[7] cgs
Temperature11,041±76[2] K
Rotational velocity (v sin i)159[8] km/s
Age100[9] Myr
Other designations
Asterope, Sterope I[10], 21 Tau, BD+24° 553, GC 4502, HD 23432, HIP 17579, HR 1151, SAO 76159[11]
Database references

21 Tauri, formally known as Asterope /əˈstrɛrəp/,[12][13] is a component of the Asterope double star in the Pleiades open cluster. 21 Tauri is the stars' Flamsteed designation. This star is potentially faintly visible to the naked eye with an apparent visual magnitude of 5.76 in ideal conditions,[2] although anybody viewing the object is likely to instead see the pair as a single elongated form of magnitude 5.6.[14] The distance to 21 Tauri can be estimated from its annual parallax shift of 7.6 mas,[1] yielding a range of around 431 light years. It is moving further from the Earth with a heliocentric radial velocity of +6 km/s.[4]

Asterope was one of the Pleiades sisters in Greek mythology. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[16] It approved the name Asterope for 21 Tauri on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[13]

21 Tauri is a blue-white hued B-type main sequence star with a stellar classification of B8 V.[3] It is a single[17] star with around three[2] times the mass of the Sun and is 100[9] million years old. The star is radiating 100[2] times the Sun's luminosity from its photosphere at an effective temperature of 11,041 K.[2] It displays an infrared excess, but this is due to reflection nebula rather than a circumstellar disk.[9]


  1. ^ a b c d 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.
  2. ^ a b c d e f g h i j Zorec, J.; Royer, F. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
  3. ^ a b Palmer, D. R.; et al. (1968), "The radial velocities spectral types and projected rotational velocities of 633 bright northern A stars", Royal Observatory Bulletin, 135: 385, Bibcode:1968RGOB..135..385P.
  4. ^ a b de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  5. ^ a b Brown, A. G. A.; et al. (Gaia collaboration) (November 2016). "Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties". Astronomy & Astrophysics. 595: A2. arXiv:1609.04172. Bibcode:2016A&A...595A...2G. doi:10.1051/0004-6361/201629512. S2CID 1828208.
  6. ^ 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.
  7. ^ David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
  8. ^ Simón-Díaz, S.; et al. (January 2017), "The IACOB project . III. New observational clues to understand macroturbulent broadening in massive O- and B-type stars", Astronomy & Astrophysics, 597: 17, arXiv:1608.05508, Bibcode:2017A&A...597A..22S, doi:10.1051/0004-6361/201628541, S2CID 3478126, A22.
  9. ^ a b c Smith, R.; Wyatt, M. C. (June 2010), "Warm dusty discs: exploring the A star 24 μm debris population", Astronomy and Astrophysics, 515: 16, arXiv:1004.0644, Bibcode:2010A&A...515A..95S, doi:10.1051/0004-6361/200913481, S2CID 118989677, A95.
  10. ^ Allen, Richard Hinckley (1963), Star names - Their Lore and Meaning, Dover Books, p. 407, retrieved 2016-09-14.
  11. ^ "21 Tau". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 21, 2018.
  12. ^ Davis, George A. (1944). "The pronunciations, derivations, and meanings of a selected list of star names". Popular Astronomy. 52: 8–30. Bibcode:1944PA.....52....8D.
  13. ^ a b Naming Stars, IAU.org, retrieved 18 June 2018.
  14. ^ Schaaf, Fred; Myers, Doug (2012), Seeing the Sky: 100 Projects, Activities & Explorations in Astronomy, Dover Books on Astronomy, Courier Corporation, p. 56, ISBN 978-0486488882
  15. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  16. ^ WG Triennial Report (2015-2018) - Star Names (PDF), p. 5, retrieved 2018-07-14.
  17. ^ Chini, R.; et al. (2012), "A spectroscopic survey on the multiplicity of high-mass stars", Monthly Notices of the Royal Astronomical Society, 424 (3): 1925–1929, arXiv:1205.5238, Bibcode:2012MNRAS.424.1925C, doi:10.1111/j.1365-2966.2012.21317.x, S2CID 119120749.