Gamma Andromedae
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 02h 03m 53.95229s[1] |
| Declination | +42° 19′ 47.0223″[1] |
| Apparent magnitude (V) | 2.27[2] |
| Characteristics | |
| Evolutionary stage | post-AGB[3] |
| Spectral type | K2+IIb[4] |
| U−B color index | +1.58[2] |
| B−V color index | +1.37[2] |
| R−I color index | +0.68[2] |
| Astrometry | |
| Radial velocity (Rv) | −11.7±0.9[5] km/s |
| Proper motion (μ) | RA: 42.32[1] mas/yr Dec.: −49.30[1] mas/yr |
| Parallax (π) | 8.30 ± 1.04[1] mas |
| Distance | approx. 390 ly (approx. 120 pc) |
| Details | |
| Mass | 23.7±0.1[6] M☉ |
| Radius | 80[7] R☉ |
| Luminosity | 2,000[7] L☉ |
| Surface gravity (log g) | 2.0[8] cgs |
| Temperature | 4,250[3] K |
| Metallicity [Fe/H] | −0.06[3] dex |
| Rotational velocity (v sin i) | < 17[2] km/s |
| Age | 6.5±0.1[6] Myr |
| Orbit[9] | |
| Primary | γ1 Andromedae |
| Companion | γ2 Andromedae |
| Period (P) | 4,748 yr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Gamma Andromedae, Latinized from γ Andromedae, is the third-brightest point of light in the northern constellation of Andromeda. It is a multiple star system approximately 350 light-years from the Earth. The system is drifting closer to the Sun with a radial velocity in the range of −12 to −14 km/s.[5]
Observation[]
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.[12]
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.[13][14] 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.[12][15]
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).[16] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[17] 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.[14]
Almach was the traditional name (also spelt as Almaach, Almaack, Almak, Almaak, or Alamak), derived from the Arabic العناق (al-‘anāq),[18] "the caracal" (desert lynx).[19] Another term for this star used by medieval astronomers writing in Arabic was رجل المسلسلة (Rijl al Musalsalah), "Foot of The [Chained] Woman".[18] 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.[20][21]
In Chinese, 天大將軍 (Tiān Dà Jiāng Jūn), 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 天大將軍一 (Tiān Dà Jiāng Jūn yī, English: the First Star of Heaven's Great General).[22]
In the Babylonian star catalogues, γ Andromedae, together with Triangulum, formed the constellation known as MULAPIN (