Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Iota Boötis is a star system in the constellation Boötes. It has the traditional name Asellus Secundus and the Flamsteed designation 21 Boötis. The primary component, Iota Boötis A, a spectroscopic binary,[citation needed] 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.