Theta Boötis

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Theta Boötis
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
Right ascension 14h 25m 11.79703s[1]
Declination +51° 51′ 02.6769″[1]
Apparent magnitude (V) 4.05[2]
Spectral type F7 V[2]
U−B color index −0.02[3]
B−V color index +0.50[2]
R−I color index 0.25
Radial velocity (Rv)−11.60[4] km/s
Proper motion (μ) RA: -235.40[1] mas/yr
Dec.: -399.07[1] mas/yr
Parallax (π)68.82 ± 0.14[1] mas
Distance47.39 ± 0.10 ly
(14.53 ± 0.03 pc)
Absolute magnitude (MV)3.25[5]
Mass1.3[2] M
Radius1.733 ± 0.011[6] R
Luminosity4.131 ± 0.096[6] L
Surface gravity (log g)4.12[2] cgs
Temperature6265 ± 41[6] K
Metallicity [Fe/H]0.02[7] dex
Rotational velocity (v sin i)29.2[8] km/s
Other designations
Asellus Primus, 23 Boötis, BD+52° 1804, FK5 531, GJ 549, HD 126660, HIP 70497, HR 5404, SAO 29137, LTT 14245.[9]
Database references

Theta Boötis (θ Boo, θ Boötis) is a main sequence star in the constellation Boötes, about 47 light years away. It has the traditional name Asellus Primus (Latin for "first donkey colt")[10] and the Flamsteed designation 23 Boötis.


θ Boötis, along with the other Aselli (ι Boo and κ Boo) and λ Boo, were Aulād al Dhiʼbah (أولاد الضّباع - aulād al dhiʼb), "the Whelps of the Hyenas".[11]

In Chinese, 天枪 (Tiān Qiāng), meaning Celestial Spear, refers to an asterism consisting of θ Boötis, κ2 Boötis and ι Boötis.[12] Consequently, θ Boötis itself is known as 天枪三 (Tiān Qiāng sān, English: the Third Star of Celestial Spear.)[13]


Theta Boötis has apparent magnitude +4.05 and belongs to the spectral class F7V. It is approximately 47 light years from Earth. From about 4300 BC until 3942 BC, it was the closest star to the celestial north pole visible to the naked eye, although it was still too dim to be regarded as a pole star.[citation needed]

There is a nearby 11th magnitude optical companion star about 70 arcseconds away. This is a class M2.5 dwarf that is separated by a minimum of 1,000 AUs. It is uncertain whether they are gravitationally bound, but they do have a common motion through space and so the two stars probably share a common origin.[14][15]


  1. ^ a b c d e van Leeuwen, F. (November 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
  2. ^ a b c d e Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M
  3. ^ Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data. SIMBAD, Bibcode:1986EgUBV........0M
  4. ^ Gontcharov, G. A. (November 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.
  5. ^ Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191.
  6. ^ a b c Boyajian, Tabetha S.; et al. (February 2012), "Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars", The Astrophysical Journal, 746 (1): 101, arXiv:1112.3316, Bibcode:2012ApJ...746..101B, doi:10.1088/0004-637X/746/1/101. See Table 10.
  7. ^ Prugniel, P.; Vauglin, I.; Koleva, M. (2011). "The atmospheric parameters and spectral interpolator for the MILES stars". Astronomy & Astrophysics. 531: A165. arXiv:1104.4952. Bibcode:2011A&A...531A.165P. doi:10.1051/0004-6361/201116769.
  8. ^ Schröder, C.; et al. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo" (PDF), Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377.
  9. ^ "28 January 2018". SIMBAD. Centre de données astronomiques de Strasbourg.
  10. ^ Star Name - R.H.Allen p.105
  11. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc, p. 105, ISBN 0-486-21079-0, retrieved 2010-12-12
  12. ^ (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.
  13. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-08-11 at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
  14. ^ Kaler, James, "Asellus Primus", Stars, University of Illinois, retrieved 2016-01-07.
  15. ^ Lépine, Sébastien; Bongiorno, Bethany (March 2007), "New Distant Companions to Known Nearby Stars. II. Faint Companions of Hipparcos Stars and the Frequency of Wide Binary Systems", The Astronomical Journal, 133 (3): 889–905, arXiv:astro-ph/0610605, Bibcode:2007AJ....133..889L, doi:10.1086/510333.

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