Iota Boötis

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ι Boötis
Boötes constellation map.svg
Red circle.svg

Location of ι Boötis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
Right ascension 14h 16m 09.92995s[1]
Declination +51° 22′ 02.0267″[1]
Apparent magnitude (V) 4.75[2] (4.73 - 4.78[3])
Spectral type A7 V[4]
U−B color index +0.06[5]
B−V color index +0.20[5]
R−I color index +0.09[5]
Variable type Delta Scuti variable[3]
Radial velocity (Rv) −18.7[6] km/s
Proper motion (μ) RA: -149.39[1] mas/yr
Dec.: +88.72[1] mas/yr
Parallax (π) 34.40 ± 0.19[1] mas
Distance 94.8 ± 0.5 ly
(29.1 ± 0.2 pc)
Absolute magnitude (MV) +2.38[7]
Mass 1.81[4] M
Radius 1.6[7] R
Luminosity 9.6[7] L
Surface gravity (log g) 4.3[7] cgs
Temperature 8,000[7] K
Metallicity [Fe/H] +0.19[8] dex
Rotational velocity (v sin i) 144[9] km/s
Other designations
Asellus Secondus,[10] 21 Boötis, BD+52°1784, FK5 528, HD 125161, HIP 69713, HR 5350, SAO 29071, Wo 9474, WDS J14162+5122
Database references
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.)

Iota Boötis (ι Boo, ι Boötis) is a star system in the constellation Boötes. It has the traditional name Asellus Secundus (Latin for "second donkey colt") and the Flamsteed designation 21 Boötis. It is approximately 95 light years from Earth.

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

In Chinese, 梗河 (Tiān Qiāng), meaning Celestial Spear, refers to an asterism consisting of ι Boötis, κ2 Boötis and θ Boötis.[12] Consequently, ι Boötis itself is known as 天槍二 (Tiān Qiāng èr, English: the Second Star of Celestial Spear.)[13]


Iota Boötis has a companion at an angular distance of 38.6 arcseconds, easily separated with binoculars.

The primary component, Iota Boötis, is a white A-type main sequence dwarf with a mean apparent magnitude of +4.75. It is classified as a Delta Scuti type variable star and its brightness varies from magnitude +4.73 to +4.78 with a stable period of 38 minutes.[7]

The companion, HD 234121, is a magnitude +8.27 main sequence star belonging to spectral class K0.[14] It is separated from ι Boo by 1,100 AU.[4]

The Washington Double Star Catalog lists a third component, a 14th magnitude star at 90 arc seconds.[14]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357 
  2. ^ 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. ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S. 
  4. ^ a b c De Rosa, R. J.; Patience, J.; Wilson, P. A.; Schneider, A.; Wiktorowicz, S. J.; Vigan, A.; Marois, C.; Song, I.; MacIntosh, B.; Graham, J. R.; Doyon, R.; Bessell, M. S.; Thomas, S.; Lai, O. (2014). "The VAST Survey - III. The multiplicity of A-type stars within 75 pc". Monthly Notices of the Royal Astronomical Society. 437 (2): 1216. Bibcode:2014MNRAS.437.1216D. arXiv:1311.7141Freely accessible. doi:10.1093/mnras/stt1932. 
  5. ^ a b c 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. 
  6. ^ Evans, D. S. (1967). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and their Applications. 30: 57. Bibcode:1967IAUS...30...57E. 
  7. ^ a b c d e f Kiss, L. L.; Alfaro, E. J.; Bakos, G.; Csak, B.; Szatmary, K. (1999). "On the monoperiodicity of the suspected delta Scuti star Iota Bootis". Information Bulletin on Variable Stars. 4698: 1. Bibcode:1999IBVS.4698....1K. 
  8. ^ Gray, R. O.; Graham, P. W.; Hoyt, S. R. (2001). "The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. II. Basic Parameters of Program Stars and the Role of Microturbulence". The Astronomical Journal. 121 (4): 2159. Bibcode:2001AJ....121.2159G. doi:10.1086/319957. 
  9. ^ Zorec, J.; Royer, F. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy & Astrophysics. 537: A120. Bibcode:2012A&A...537A.120Z. arXiv:1201.2052Freely accessible. doi:10.1051/0004-6361/201117691. 
  10. ^ Star Name - R.H.Allen p.105
  11. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: 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. ^ a b 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. 

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