Magnitude 4.75 Apparent magnitude (V) 4.75 | Constellation Boötes | |
 | ||
Similar Kappa Boötis, 38 Boötis, Mu Boötis, Phi Boötis, Gamma Boötis | ||
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".
In Chinese, 梗河 (Tiān Qiāng), meaning Celestial Spear, refers to an asterism consisting of ι Boötis, κ2 Boötis and θ Boötis. Consequently, ι Boötis itself is known as 天槍二 (Tiān Qiāng èr, English: the Second Star of Celestial Spear.)
Components
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.
The companion, HD 234121, is a magnitude +8.27 main sequence star belonging to spectral class K0. It is separated from ι Boo by 1,100 AU.
The Washington Double Star Catalog lists a third component, a 14th magnitude star at 90 arc seconds.