An image of γ Andromedae as it appears in a small telescope
In 1778, German physicistJohann Tobias Mayer discovered that γ Andromedae is adouble star. When examined in a smalltelescope, 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 nameAlmach/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 atriple star system. What appears as a single star to the naked eye is thus a quadruple star system.[11][14]
γ Andromedae (Latinised toGamma Andromedae) is the system'sBayer designation;γ1 andγ2 Andromedae those of its two constituents. The designations of those constituents asGamma Andromedae A andB derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiplestar systems, and adopted by theInternational Astronomical Union (IAU).[15] In 2016, the IAU organized aWorking Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN approved the nameAlmach 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 asAlmaach,Almaack,Almak,Almaak, orAlamak), derived from theArabicالعناق (al-‘anāq),[17] "thecaracal" (desert lynx).[18] Another term for this star used by medieval astronomers writing in Arabic wasرجل المسلسلة (Rijl al Musalsalah), "Foot of The [Chained] Woman".[17] In the catalogue of stars in theCalendarium ofAl Achsasi al Mouakket, this star was designated الخامس النعامة (Al Khamis al Na'amah), which was translated intoLatin as Quinta Struthionum, meaningthe fifth ostrich.[19][20]
In theBabylonian star catalogues, γ Andromedae, together withTriangulum, formed the constellation known asMULAPIN (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.[6]
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 anA-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 higheccentricity of 0.927.[28] Spectrograms taken from 1957 to 1959 revealed that γ Andromedae B was itself aspectroscopic binary, composed of twoB-type main-sequence stars orbiting each other with a period of 2.67 days.[31] The two orbits may becoplanar.[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.
^abTokovinin, A. A."HIP 9640".Multiple Star Catalogue. Archived fromthe original on 2020-10-02. Retrieved2019-11-19.
^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.
