Iota Boötis

From Wikipedia, the free encyclopedia
  (Redirected from Iota Bootis)
Jump to: navigation, search
Iota Boötis
Diagram showing star positions and boundaries of the Boötes constellation and its surroundings
Cercle rouge 100%.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]
Spectral type A9 V[2]
U−B color index 0.06
B−V color index 0.2
R−I color index 0.09
Variable type Delta Scuti variable
Radial velocity (Rv) -18.7 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)
Mass 2.3[2] M
Radius 1.0[2] R
Luminosity 11[2] L
Surface gravity (log g) 4.80[2] cgs
Temperature 10,560 ± 340[2] K
Other designations
Asellus Secondus, 21 Boötis, BD+52°1784, FK5 528, HD 125161, HIP 69713, HR 5350, SAO 29071, Wo 9474.
Database references
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.)
Database references

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")[3] and the Flamsteed designation 21 Boötis.

This star, along with the other Aselli (θ Boo and κ Boo) and λ Boo, were Al Aulād al Dhiʼbah (ألعولد ألذعب - al aulād al dhiʼb), "the Whelps of the Hyenas".[4]

In Chinese, 梗河 (Tiān Qiāng), meaning Celestial Spear, refers to an asterism consisting of ι Boötis, κ2 Boötis and θ Boötis.[5] Consequently, ι Boötis itself is known as 天槍二 (Tiān Qiāng èr, English: the Second Star of Celestial Spear.)[6]

Iota Boötis is a double star, with components at an angular distance of 38.6 arcseconds, easily separated with binoculars. It is approximately 97 light years from Earth.


The primary component, Iota Boötis A, 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. The companion, Iota Boötis B, is a magnitude +8.27 star belonging to spectral class A2.


  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 f g 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. ^ Star Name - R.H.Allen p.105
  4. ^ 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 
  5. ^ (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.
  6. ^ (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.

External links[edit]