There are five visible companions to Mu Cassiopeiae listed in the
Washington Double Star Catalog. All are distant background objects fainter than 11th magnitude. The brightest of these is catalogued as component B, but the very high
proper motion of Mu Cassiopeiae has caused it to almost double its distance from B. There are now two other stars brighter than magnitude 10 that are closer to Mu Cassiopeiae, although they are also background objects. The companions C and D are separated from each-other by four
arc seconds and form a binary system about away. Mu Cassiopeiae itself is known as an
astrometric binary, a star that is observed to oscillate due to the gravitational influence of an unseen companion, and that companion has now been resolved. In 1961, the close binary nature of this system was discovered by Nicholas E. Wagman at the
Allegheny Observatory. Since then the orbital elements of the two stars have been fairly well established. The two stars are separated by a
semimajor axis of 7.61
AUs with distance range of 3.3-11.9
AUs. In 1966, the individual components were first resolved by the American astronomer Peter A. Wehinger using the 84-inch reflector at the
Kitt Peak National Observatory, allowing an initial estimate of separate masses. The companion is over six magnitudes (330 times) fainter than the primary star, and it is presumed to be a
red dwarf, a class M main sequence or subdwarf star. ==See also==