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| Gamma Andromedae | |
|---|---|
| Name | Gamma Andromedae |
| Other names | Almach, Almaak, γ Andromedae, Gam And |
| Constellation | Andromeda |
| Epoch | J2000 |
| Ra | 00h 08m 23.2s |
| Dec | +29° 05′ 25″ |
| App mag v | 2.10 (system) |
| Spectral type | K2II + B8V (composite) |
| Parallax | 29.46 mas |
| Distance | 33.9 pc |
| Radial velocity | −12 km/s |
| Components | γ And A, γ And Ab, γ And B, γ And C |
Gamma Andromedae Gamma Andromedae, traditionally known as Almach or Almaak, is a prominent multiple star system in the northern constellation Andromeda notable for its striking visual contrast and role as a navigational beacon in historical star catalogs. The system has been studied across disciplines from observational astronomy to stellar astrophysics, and it appears in classical catalogs maintained by institutions such as the Hipparcos and Tycho missions and the Washington Double Star Catalog.
The traditional name Almach or Almaak is recorded in medieval Arabic star lore and preserved in modern compilations by the International Astronomical Union's Working Group on Star Names, alongside Bayer designation γ Andromedae and Flamsteed-style references found in catalogs compiled by John Flamsteed and later by Johann Bayer. Historical references to the star occur in the star lists of Ptolemy and in medieval compilations transmitted through scholars associated with Al-Sufi and the Baghdad observatory tradition. Modern observational programs reference the system using catalog entries from Henry Draper Catalogue, Hipparcos Catalogue, Bright Star Catalogue, Simbad and the General Catalogue of Variable Stars when applicable.
Gamma Andromedae is a hierarchical multiple system consisting of a bright primary pair and at least two distant companions cataloged in the Washington Double Star Catalog. The primary component A is itself a spectroscopic pair labeled A and Ab in interferometric studies conducted with instruments at Palomar Observatory and European Southern Observatory interferometers; the visually striking secondary B (often called the orange-yellow giant) is the classical visual companion resolved by observers such as William Herschel and later measured by observers working with the Mount Wilson Observatory and the Royal Greenwich Observatory. Additional faint components C and D have been cataloged by surveys including the Two Micron All Sky Survey and follow-up work by research teams associated with Kitt Peak National Observatory and Lowell Observatory.
The visually dominant star in the pair displays an orange hue corresponding to a late-type spectral energy distribution, while the blue-white companion shows a contrasting early-type spectrum; this color contrast has been noted in atlases produced by Heinrich Olbers and in photographic plates from the Harvard College Observatory. The primary giant has parameters derived from model fits using data from GAIA and spectrophotometry reductions developed at European Space Agency centers, yielding estimates for luminosity, radius, and effective temperature based on stellar evolution codes such as those distributed by the Geneva Observatory and the Padova group. Masses and ages have been constrained by comparisons to isochrones produced by groups at University of Cambridge and University of California, Berkeley.
Spectroscopic classification assigns the orange primary to a late-K bright giant luminosity class based on work by spectral compilers like Morgan, Keenan, and collaborators, while the blue companion is classified as a main-sequence B-type star in line with standards maintained at Harvard and refined by observers at McDonald Observatory. High-resolution spectroscopy from instruments at Keck Observatory and ESO Very Large Telescope has revealed line profiles used to infer rotation rates, chemical abundances, and radial-velocity variability, with analysis methods developed by teams at Harvard-Smithsonian Center for Astrophysics and Max Planck Institute for Astronomy.
The visual pair exhibits an orbital motion characterized by measures spanning centuries, compiled and analyzed by astrometric researchers at US Naval Observatory and in catalogues by Struve and F. G. W. von Struve lineages; more recent interferometric solutions from groups at CHARA Array and NPOI provided refined orbital elements including inclination, period, and eccentricity. The spectroscopic subcomponent Ab introduces additional dynamical complexity that has been modeled by teams using dynamical codes from NASA and the European Southern Observatory, and the system's dynamical mass estimates have been cross-checked with mass-luminosity relations developed at Caltech and Princeton University.
Parallax and proper motion measurements from the Hipparcos mission and later from Gaia provide precise distance and tangential velocity data, placing the system at roughly 110 light-years from the Sun in the northern sky near constellations such as Pegasus and close to the Andromeda Galaxy in projection. Radial velocity monitoring by teams at Lick Observatory and Cerro Tololo Inter-American Observatory links the system's space motion to kinematic populations studied by researchers at European Southern Observatory and the Max Planck Institute.
Gamma Andromedae's striking color contrast and brightness made it a target for early telescopic observers including Galileo Galilei and later catalogers such as John Herschel and William Herschel, appearing in star atlases by Alexander Jamieson and in navigation charts used by explorers associated with Royal Navy voyages. The star features in mythological and literary treatments tied to the constellation Andromeda recorded by classical authors like Hesiod and later revived in Renaissance star maps by Johannes Kepler and Tycho Brahe's successors. Modern cultural references appear in planetarium programming at institutions such as the American Museum of Natural History and in educational outreach by the Royal Astronomical Society and the Astronomical Society of the Pacific.
Category:Andromeda (constellation) Category:Multiple stars