Gamma Andromedae

Gamma Andromedae is a multiple star system in the northern constellation of Andromeda. It is the third-brightest star in the constellation, after Alpheratz and Mirach. Its identifier is a Bayer designation that is Latinized from γ Andromedae, and is abbreviated Gam¹ And or γ¹ And, respectively. The system has the proper name Almach, pronounced Template:IPAc-en. Based on parallax measurements, it is estimated to be about 390 light-years distant. The system is drifting closer to the Sun with a radial velocity of Template:Val.<ref name=rv/>

Observation

File:Almach double star.jpg

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.<ref name=burnham>Template:Cite book</ref>

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 Template:IPAc-en, which was used as the traditional name of the naked eye star, and thus the system as a whole.<ref name=Kunitzsch>Template:Cite book</ref><ref name=IAU-LSN>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name=burnham/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

File:Almach dpeach crop.jpg

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).<ref name=planetnaming>Template:Cite arXiv</ref> In 2016, the IAU organized a Working Group on Star Names (WGSN)<ref name=WGSN>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name=IAU-LSN/>

Almach was the traditional name (also spelt as Almaach, Almaack, Almak, Almaak, or Alamak), derived from the Arabic العناق (al-‘anāq),<ref name=allen/> "the caracal" (desert lynx).<ref>Template:Cite book</ref> Another term for this star used by medieval astronomers writing in Arabic was رجل المسلسلة (Rijl al Musalsalah), "Foot of The [Chained] Woman".<ref name=allen/> 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.<ref>Template:Cite journal</ref><ref>Template:Cite book</ref>

In Chinese, {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning Heaven's Great General, refers to an asterism consisting of γ Andromedae, φ Persei, 51 Andromedae, 49 Andromedae, χ Andromedae, υ Andromedae, τ Andromedae, 56 Andromedae, β Trianguli, γ Trianguli and δ Trianguli. Consequently, the Chinese name for γ Andromedae itself is {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, Template:Langx).<ref>Template:In lang AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 10 日 Template:Webarchive</ref>

In the Babylonian star catalogues, γ Andromedae, together with Triangulum, formed the constellation known as ^MULAPIN (Template:Script) "The Plough".<ref>Template:Cite journal</ref> Astrologically, this star was considered "honourable and eminent".<ref name=Olcott>Template:Cite book</ref>

Stellar properties

File:Gamma Andromedae Components Black.svg

Gamma Andromedae Components

γ¹ Andromedae A is a massive bright giant star with a spectral classification of K2+IIb.<ref name=perkins1989/> The star has an apparent visual magnitude of approximately 2.26.<ref name=bsc1/> It has been classified as a candidate post-asymptotic giant branch (AGB) star.<ref name=Rao_et_al_2012/> However, it does not display a chemical enhancement of s-process elements typical of an AGB star.<ref name=Giridhar_Arellano_Ferro_2005>Template:Cite journal</ref>

The γ² Andromedae BC sub-system, with an overall apparent visual magnitude of 4.84,<ref name=bsc2/> is 9.6 arcseconds away from γ¹ Andromedae at a position angle of 63 degrees.<ref name=wds0/>

γ¹ and γ² have an orbital period of approximately 5,000 years.<ref name=orb1/>

In October 1842, Wilhelm Struve found that γ² Andromedae was itself a double star whose components were separated by less than an arcsecond.<ref name=allen>Template:Cite book</ref> 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.<ref name=bsc2/> They have an orbital period of about 64 years and a high eccentricity of 0.927.<ref name=orb2/> 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.<ref name=specbin>Template:Cite journal</ref> The two orbits may be coplanar.<ref name=orb2/> As of 2019, the angular distance between the B and C stars was 0.16 arcsecond.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Almach as a name

Template:USS was the name of a United States navy ship.

See also

• NGC 752

External links

• Almaak (Gamma Andromedae) at The Internet Encyclopedia of Science
• Image ALMACH
• Almaak on AstroDwarf
• Template:WikiSky