An image of γ Andromedae as it appears in a small telescope
In 1778, German physicist Johann Tobias Mayer discovered that γ Andromedae is a double star. When examined in a small telescope, it appears to be a bright, golden-yellow star next to a dimmer, indigo-blue star, separated by approximately 10 arcseconds. The pair is often considered by stargazers to be a beautiful double star with a striking contrast of color.[11]
The brighter member, γ1 Andromedae, is the primary of the system, and is thus designated component γ Andromedae A. It has the official proper name Almach/ˈælmæk/, which was used as the traditional name of the naked eye star, and thus the system as a whole.[12][13] The fainter secondary is γ2 Andromedae or γ Andromedae B. It was later discovered that γ2 Andromedae is itself a triple star system. What appears as a single star to the naked eye is thus a quadruple star system.[11][14]
Almach star system showing A, B and C components
Nomenclature
γ Andromedae (Latinised to Gamma Andromedae) is the system's Bayer designation; γ1 and γ2 Andromedae those of its two constituents. The designations of those constituents as Gamma Andromedae A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[15] In 2016, the IAU organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN approved the name Almach for the component Gamma Andromedae A on 20 July 2016 and it is now so included in the List of IAU-approved Star Names.[13]
Almach was the traditional name (also spelt as Almaach, Almaack, Almak, Almaak, or Alamak), derived from the Arabicالعناق (al-‘anāq),[17] "the caracal" (desert lynx).[18] Another term for this star used by medieval astronomers writing in Arabic was رجل المسلسلة (Rijl al Musalsalah), "Foot of The [Chained] Woman".[17] In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated الخامس النعامة (Al Khamis al Na'amah), which was translated into Latin as Quinta Struthionum, meaning the fifth ostrich.[19][20]
In the Babylonian star catalogues, γ Andromedae, together with Triangulum, formed the constellation known as MULAPIN (𒀯𒀳) "The Plough".[22] Astrologically, this star was considered "honourable and eminent".[23]
γ1 and γ2 have an orbital period of approximately 5,000 years.[8]
In October 1842, Wilhelm Struve found that γ2 Andromedae was itself a double star whose components were separated by less than an arcsecond.[17] The components are an object of apparent visual magnitude 5.5, γ Andromedae B, and an A-type main-sequence star with apparent visual magnitude 6.3, γ Andromedae C.[25] They have an orbital period of about 64 years and a high eccentricity of 0.927.[28] Spectrograms taken from 1957 to 1959 revealed that γ Andromedae B was itself a spectroscopic binary, composed of two B-type main-sequence stars orbiting each other with a period of 2.67 days.[31] The two orbits may be coplanar.[28] As of 2019, the angular distance between the B and C stars was 0.16 arcsecond.[32]
^ abcWilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
^Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Publishing Company. ISBN978-1-931559-44-7.
^Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
^Rogers, J. H. (1998). "Origins of the ancient constellations: I. The Mesopotamian traditions". Journal of the British Astronomical Association. 108: 9. Bibcode:1998JBAA..108....9R.
