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Omicron Andromedae
Variable star in the constellation of Andromeda From Wikipedia, the free encyclopedia
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Omicron Andromedae, also named Alfarasalkamil,[17] is a star system in the northern constellation Andromeda. Its Bayer designation is Latinized from ο Andromedae, and is abbreviated Omi And or ο And, respectively. Based on parallax measurements, it is located at a distance of approximately 690 light years from Earth.[8] The system as a whole is classified as a blue-white B-type giant,[4] with a typical combined apparent magnitude of +3.62.[2] This is sufficiently bright that the star can be viewed with the naked eye on a dark night.
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Nomenclature
This star was in the head of the traditional Arabic constellation Al Faras al Kamil, the Complete Horse, as opposed to Pegasus which is the front half of a horse.[18] The IAU Working Group on Star Names approved the name Alfarasalkamil for this star on 8 May 2025 and it is now so entered in the IAU Catalog of Star Names.[17]
It was also the brightest star of the obsolete constellation Honores Friderici.[19]
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System
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,[15] although the binarity of the primary star is in doubt.[12] This star system has a peculiar velocity of 34.5 ± 5.9 km/s, which qualifies it as a runaway star.[15]
The components A and B were first resolved in 1949, when they were reported to be separated by less than 0.1".[20] In 1975 they were separated by 0.375"[13] and by 2014 by only 0.21".[21] 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,[11] although the existence of this companion is now doubted.[12]
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.[13] Eventually, it was settled that component B was a close spectroscopic binary.[11]
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Properties
Omicron Andromedae is a Gamma Cassiopeiae type variable 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] Rapid variations in its spectrum have been reported.[23]
Spectral lines similar to an A2 star are also detectable in the spectrum and these are thought to originate in the B component.[5]
References
External links
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