Astronomy:Tau Scorpii

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Tau Scorpii
Diagram showing star positions and boundaries of the Scorpius constellation and its surroundings
Cercle rouge 100%.svg
Location of τ Scorpii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension  16h 35m 52.95285s[1]
Declination −28° 12′ 57.6615″[1]
Apparent magnitude (V) +2.82[2]
Spectral type B0.2 V[3]
U−B color index −1.039[2]
B−V color index −0.252[2]
Radial velocity (Rv)+2.0[4] km/s
Proper motion (μ) RA: −9.89[1] mas/yr
Dec.: −22.83[1] mas/yr
Parallax (π)6.88 ± 0.53[1] mas
Distance470 ± 40 ly
(150 ± 10 pc)
Absolute magnitude (MV)−4.2[5]
Mass15.0 ± 0.1,[6] 14.5–14.7[7] M
Radius6.5[3] R
Luminosity20,400[7] L
Surface gravity (log g)4.24[8] cgs
Temperature31,440,[9] 29,850[7] K
Metallicity [Fe/H]−0.14[8] dex
Rotation41 days[10]
Rotational velocity (v sin i)24[11] km/s
Age5.7 ± 1.0,[6] 5[7] Myr
Other designations
Paikauhale (star A), Alniyat, Al Niyat τ Sco, 23 Sco, FK5 620, GC 22303, HD 149438, HIP 81266, HR 6165, SAO 184481.[12]
Database references

Tau Scorpii (τ Sco, τ Scorpii), formally known as Paikauhale /ˌpkˈhɑːl/, is a star in the southern zodiac constellation of Scorpius. The apparent visual magnitude of Tau Scorpii is +2.8,[2] while parallax measurements yield a distance estimate of roughly 470 light-years (150 parsecs) from Earth.[1]


Surface magnetic field of Tau Scorpii as reconstructed by means of Zeeman–Doppler imaging

Compared to the Sun, Tau Scorpii is a massive OB star with 15[6] times the Sun's mass and more than six times the radius of the Sun.[3] It is radiating about 20,400[7] times the Sun's luminosity from its outer envelope at an effective temperature of 31,440 K.[9] This gives it the blue-white hue characteristic of B-type stars.[13] As yet there is no evidence of a companion in orbit around τ Sco.[14] It is a magnetic star whose surface magnetic field was mapped by means of Zeeman–Doppler imaging.[15] Tau Scorpii is rotating relatively slowly with a period of 41 days.[10]

The spectrum of this star shows triply ionized oxygen (O IV) that is being generated by X-rays and the Auger ionization effect. Observations with the ROSAT space telescope showed it has a higher energy (harder) X-ray spectrum than is usual for B0 V stars. Over the energy range 0.8–1.2 keV, its X-ray luminosity is Lx = 1.8 × 1031 erg s−1 with a large Lx to Lbol of log Lx/Lbol = –6.53 from ASCA measurements. ROSAT measurements showed a log Lx/Lbol ≃ –5.93 for the range 0.1–2.4 keV.[14] The hard component of the X-ray spectrum from τ Sco as studied with XMM-Newton supports the presence of in-falling clumps of plasma in τ Sco.[14]

This star is a proper motion member of the Upper Scorpius subgroup of the Scorpius-Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.[5][7] The Upper Scorpius subgroup contains thousands of young stars with mean age 11 million years at average distance of 470 light years (145 parsecs)[7] A more recent analysis[7] of the HR diagram position for Tau Scorpii estimates its effective temperature to be 29,850 kelvins with a luminosity of 20,400 Suns, consistent with an isochronal age of 5 million years and an estimated mass of 14.5–14.7 solar masses.


τ Scorpii (Latinised to Tau Scorpii) is the star's Bayer designation.

Tau Scorpii and Sigma Scorpii together bore the traditional name Al Niyat (or Alniyat) derived from the Arabic النياط al-niyāţ "the arteries" and referring to their position flanking the star Antares, the scorpion's heart, with Tau Scorpii being the star to the south.[16]

Paikauhale is the Hawaiian name for Tau Scorpii.[17][18] In the Hawaiian dictionary by Pukuʻi & Elbert (1986), the word paikauhale [ˈpəiˈkəuˈhale] is defined as to go gadding about from house to house. In another Hawaiian dictionary (H.W. Kent, 1993, "Treasury of Hawaiian Words in One Hundred and One Categories", p.367), paikauhale is defined as Vagabond owning no home; house-to-house wanderer.

In 2016, the IAU organized a Working Group on Star Names (WGSN)[19] to catalog and standardize proper names for stars. The WGSN approved the name Paikauhale for the star A on 10 August 2018 and it is now so included in the List of IAU-approved Star Names.[20] The name Alniyat was given to Sigma Scorpii.

Cultural signification

The indigenous Boorong people of northwestern Victoria saw this star (together with σ Sco) as wives of Djuit (Antares).[21]

In Chinese, 心宿 (Xīn Xiù), meaning Heart, refers to an asterism consisting of τ Scorpii, σ Scorpii and Antares.[22] Consequently, the Chinese name for τ Scorpii itself is 心宿三 (Xīn Xiù sān), "the Third Star of Heart".[23]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode2007A&A...474..653V 
  2. 2.0 2.1 2.2 2.3 Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A Photometric Investigation of the Scorpio-Centaurus Association", Astrophysical Journal Supplement 15: 459, doi:10.1086/190168, Bibcode1968ApJS...15..459G 
  3. 3.0 3.1 3.2 Howk, J. Christopher et al. (May 2000), "Stagnation and Infall of Dense Clumps in the Stellar Wind of τ Scorpii", The Astrophysical Journal 534 (1): 348–358, doi:10.1086/308730, Bibcode2000ApJ...534..348H 
  4. Wielen, R. et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg 35 (35): 1, Bibcode1999VeARI..35....1W 
  5. 5.0 5.1 de Geus, E. J.; de Zeeuw, P. T.; Lub, J. (June 1989), "Physical parameters of stars in the Scorpio-Centaurus OB association", Astronomy and Astrophysics 216 (1–2): 44–61, Bibcode1989A&A...216...44D 
  6. 6.0 6.1 6.2 Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode2011MNRAS.410..190T 
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 Mark J. Pecaut et al. (February 2012). "A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association". Astrophysical Journal 746 (2): 154. doi:10.1088/0004-637X/746/2/154. Bibcode2012ApJ...746..154P. 
  8. 8.0 8.1 Kilian, J. (February 1994), "Chemical abundances in early B-type stars. 5: Metal abundances and LTE/NLTE comparison", Astronomy and Astrophysics 282 (3): 867–873, Bibcode1994A&A...282..867K 
  9. 9.0 9.1 Zorec, J. et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics 501 (1): 297–320, doi:10.1051/0004-6361/200811147, Bibcode2009A&A...501..297Z 
  10. 10.0 10.1 Strassmeier, Klaus G. (September 2009), "Starspots", The Astronomy and Astrophysics Review 17 (3): 251–308, doi:10.1007/s00159-009-0020-6, Bibcode2009A&ARv..17..251S 
  11. 6165, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID [1]. Accessed on line February 8, 2013.
  12. "tau Sco -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg),, retrieved 2010-08-01 
  13. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004,, retrieved 2012-01-16 
  14. 14.0 14.1 14.2 Mewe, R. et al. (2003), "High-resolution X-ray spectroscopy of τ Scorpii (B0.2V) with XMM-Newton", Astronomy & Astrophysics 398 (1): 203–11, doi:10.1051/0004-6361:20021577, Bibcode2003A&A...398..203M, 
  15. Donati, J.-F. et al. (2006), "The surprising magnetic topology of τ Sco: fossil remnant or dynamo output?", Monthly Notices of the Royal Astronomical Society 370 (2): 629–644, doi:10.1111/j.1365-2966.2006.10558.x, Bibcode2006MNRAS.370..629D 
  16. Allen, Richard Hinckley (1963) [1899]. Star Names: Their Lore and Meaning (Reprint ed.). New York City , NY: Dover Publications Inc.. p. 371. ISBN 0-486-21079-0. 
  17. Kawena, Johnson, & Ruggles, 2015, "Na Inoa Hoku: Hawaiian and Pacific Star Names", p.201
  18. Puku'i & Elbert, 1986, "Hawaiian Dictionary: Hawaiian-English, English-Hawaiian", p.31
  19. "IAU Working Group on Star Names (WGSN)". Retrieved 17 September 2018. 
  20. "IAU Catalog of Star Names". International Astronomical Union. Retrieved 2018-09-17. 
  21. Hamacher, Duane W. et al. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae". Journal of Astronomical History & Heritage 13 (3): 220–34. Bibcode2010JAHH...13..220H. 
  22. (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.
  23. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 , Hong Kong Space Museum. Accessed on line November 23, 2010.

Coordinates: Sky map 16h 35m 52.9537s, −28° 12′ 57.658″