Omicron Andromedae is a multiple star containing at least three components. It may consist of two close pairs in a wider orbit, making a four-star system,[14] although the binarity of the primary star is in doubt.[11] This star system has a peculiar velocity of 34.5 ± 5.9 km/s.[14]
The components A and B were first resolved in 1949, when they were reported to be separated by less than 0.1".[16] In 1975 they were separated by 0.375"[12] and by 2014 by only 0.21".[17] An orbit has been derived with a period of 118 years.[9] The companion is 2.3 magnitudes fainter than the primary star.[5]
In 1975, a companion was discovered by speckle interferometry only 0.05" from component A.[5] Components Aa and Ab orbit every 5.6 years,[10] although the existence of this companion is now doubted.[11]
A spectroscopic binary in the system was suspected and in 1988 it was confirmed. Although a clear 33.01 day period was seen, it was unclear which component was the pair seen in the spectrum.[12] Eventually, it was settled that component B was a close spectroscopic binary.[10]
Omicron Andromedae is a Gamma Cassiopeiae typevariable star and the system's brightness varies from magnitude +3.58 to +3.78. The variable component is the brightest and most massive star in the system, Aa.[3] Omicron Andromedae also shows variations with a period of about a day, similar to a β Lyrae-type eclipsing variable, but these are thought to be intrinsic to one of the components and not due to eclipses.[6]
The spectrum is predominantly that of a B6 giant star, from the brightest component in the system. It is a shell star and the spectrum contains emission lines with variable profiles.[5]
Spectral lines similar to an A2 star are also detectable in the spectrum and these are thought to originate in the B component.[5]
^ abcNicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Observatory. Bibcode:1978ppch.book.....N.
^ abcSamus, 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: B/gcvs. Bibcode:2009yCat....102025S.
^Slettebak, A (1982). "Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars". Astrophysical Journal Supplement Series. 50: 55. Bibcode:1982ApJS...50...55S. doi:10.1086/190820.
^ abcZhuchkov, R. Ya; Malogolovets, E. V.; Kiyaeva, O. V.; Orlov, V. V.; Bikmaev, I. F.; Balega, Yu.Yu; Safina, D. I. (2010). "Physical parameters and dynamical properties of the multiple star o and". Astronomy Reports. 54 (12): 1134–1149. Bibcode:2010ARep...54.1134Z. doi:10.1134/S1063772910120061. S2CID121960504.