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Gamma Andromedae

Coordinates: Sky map 02h 03m 53.9531s, +42° 19′ 47.009″
From Wikipedia, the free encyclopedia
γ1 Andromedae
(γ Andromedae A)
Location of γ Andromedae (circled)
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]
Evolutionary stage Candidate 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]
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 mas[1]
Distanceapprox. 390 ly
(approx. 120 pc)
Radius97[6] R
Luminosity2,000[7] L
Surface gravity (log g)1.03[8] cgs
Temperature4,248[8] K
Metallicity [Fe/H]−0.06[3] dex
Rotational velocity (v sin i)< 17[2] km/s
Primaryγ1 Andromedae
Companionγ2 Andromedae
Period (P)4,748 yr
Other designations
Almach, Almaach, Almak, Almaak, Alamak, γ1 And, Gamma1 Andromedae, Gamma1 And, γ Andromedae A, γ And A, Gamma Andromedae A, Gamma And A, 57 Andromedae A, 57 And A, BD+41 395, FK5 73, GC 2477, HD 12533, HIP 9640, HR 603, SAO 37734, PPM 44721, ADS 1630 A, CCDM J02039+4220A, WDS 02039+4220A[2][10][11]
Database references

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 Earth. The system is drifting closer to the Sun with a radial velocity in the range of −12 to −14 km/s.[5]


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.[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]


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 IAU 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 (𒀯𒀳) "The Plough".[23] Astrologically, this star was considered "honourable and eminent".[24]

Stellar properties[edit]

Gamma Andromedae Components
γ2 Andromedae
(γ Andromedae BC)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Andromeda
Right ascension 02h 03m 54.720s (B)[25]
Declination +42° 19′ 51.41″ (B)[25]
Apparent magnitude (V) 4.84 (BC combined)

5.5 (B)
6.3 (C)[26]

Spectral type B9.5V/B9.5V (B)

A0V (C)[27]

U−B color index −0.12[26]
B−V color index +0.03[26]
Radial velocity (Rv)−14.0±5[5] km/s
Proper motion (μ) RA: 30.021[28] mas/yr
Dec.: −51.640[28] mas/yr
Parallax (π)12.5653 ± 0.5881 mas[28]
Distance260 ± 10 ly
(80 ± 4 pc)
Primaryγ2 And B
Period (P)63.67±1.0 yr
Semi-major axis (a)0.302±0.001
Eccentricity (e)0.927±0.03
Inclination (i)109.8±5.0°
Longitude of the node (Ω)109.6±5.0°
Periastron epoch (T)2015.5±1.5 MJD
Argument of periastron (ω)
Position (relative to γ1 And)
Epoch of observation2004
Angular distance9.6 [11]
Position angle63° [11]
Other designations
Database references

γ1 Andromedae A is a massive bright giant star with a spectral classification of K2+IIb.[4] The star has an apparent visual magnitude of approximately 2.26.[2] The star has been classified as a candidate post-asymptotic giant branch star.[3] However, it does not display a chemical enhancement of s-process elements typical of an AGB star.[31]

γ2 Andromedae BC, with an overall apparent visual magnitude of 4.84,[26] is 9.6 arcseconds away from γ1 Andromedae at a position angle of 63 degrees.[11]

γ1 and γ2 have an orbital period of approximately 5,000 years.[9]

In October 1842, Wilhelm Struve found that γ2 Andromedae was itself a double star whose components were separated by less than an arcsecond.[18] 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.[26] They have an orbital period of about 64 years and a high eccentricity of 0.927.[29] 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.[32] The two orbits may be coplanar.[29] As of 2019, the angular distance between the B and C stars was 0.16 arcsecond.[33]

Almach as a name[edit]

USS Almaack (AKA-10) was the name of United States navy ship.

See also[edit]


  1. ^ a b c d e van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
  2. ^ a b c d e f g Hoffleit, Dorrit; Jaschek, Carlos (1991). The Bright star catalogue. Bibcode:1991bsc..book.....H. "database entry". CDS. Retrieved 2019-11-19.
  3. ^ a b c Rao, S. Sumangala; Giridhar, Sunetra; Lambert, David L. (January 2012). "Chemical composition of a sample of candidate post-asymptotic giant branch stars". Monthly Notices of the Royal Astronomical Society. 419 (2): 1254–1270. Bibcode:2012MNRAS.419.1254R. doi:10.1111/j.1365-2966.2011.19780.x.
  4. ^ a b Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373, S2CID 123149047.
  5. ^ a b c Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
  6. ^ Cruzalèbes, P.; Petrov, R. G.; Robbe-Dubois, S.; Varga, J.; Burtscher, L.; Allouche, F.; Berio, P.; Hofmann, K. -H.; Hron, J.; Jaffe, W.; Lagarde, S.; Lopez, B.; Matter, A.; Meilland, A.; Meisenheimer, K. (2019-12-01). "A catalogue of stellar diameters and fluxes for mid-infrared interferometry". Monthly Notices of the Royal Astronomical Society. 490: 3158–3176. arXiv:1910.00542. doi:10.1093/mnras/stz2803. ISSN 0035-8711.
  7. ^ Jim Kaler. "Almach". Stars. Retrieved 2019-11-19.
  8. ^ a b Luck, R. Earle (2014-06-01). "Parameters and Abundances in Luminous Stars". The Astronomical Journal. 147: 137. doi:10.1088/0004-6256/147/6/137. ISSN 0004-6256.
  9. ^ a b Tokovinin, A. A. "HIP 9640". Multiple Star Catalogue. Archived from the original on 2020-10-02. Retrieved 2019-11-19.
  10. ^ "* gam01 And". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved August 19, 2008.
  11. ^ a b c d e Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920. "02039+4220, components A-BC". The Washington Double Star Catalog. Archived from the original on 2006-02-20. Retrieved 2019-11-19.
  12. ^ a b Robert Burnham (1 January 1978). Andromeda-Cetus. Courier Corporation. ISBN 978-0-486-23567-7.
  13. ^ 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. ISBN 978-1-931559-44-7.
  14. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  15. ^ A. A. Tokovinin. "MSC - a catalogue of physical multiple stars". CDS. Retrieved 2019-11-19.
  16. ^ 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].
  17. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  18. ^ a b c Richard Hinckley Allen (1899). Star-names and Their Meanings. New York: G.E. Stechert. pp. 36–37.
  19. ^ Ridpath, Ian (1988). Star Tales. James Clarke & Co. ISBN 0-7188-2695-7.
  20. ^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
  21. ^ Richard H. Allen (28 February 2013). Star Names: Their Lore and Meaning. Courier Corporation. ISBN 978-0-486-13766-7. η Cet (Deneb Algenubi), θ Cet (Deneb Algenubi), τ Cet (Durre Menthor), ζ Cet (Baten Kaitos), and υ Cet, were Al Naʽāmāt, the Hen Ostriches.
  22. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 10 日 Archived 2011-07-16 at the Wayback Machine
  23. ^ 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.
  24. ^ William Tyler Olcott (December 1985). Star Lore of All Ages. Health Research Books. ISBN 978-0-7873-1096-7.
  25. ^ a b Component 2, HIP 9640, database entry, Hipparcos catalogue, CDS ID I/239.
  26. ^ a b c d e Hoffleit, Dorrit; Jaschek, Carlos (1991). The Bright star catalogue. Bibcode:1991bsc..book.....H. "database entry". CDS. Retrieved 2019-11-19.
  27. ^ Entry 02039+4220, discoverer code STT  38BC, The Washington Double Star Catalog Archived 2006-02-20 at the Wayback Machine, United States Naval Observatory. Accessed on line August 19, 2008.
  28. ^ a b c Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  29. ^ a b c Docobo, J. A.; Ling, J. F. (April 2007). "Orbits and System Masses of 14 Visual Double Stars with Early-Type Components". The Astronomical Journal. 133 (4): 1209–1216. Bibcode:2007AJ....133.1209D. doi:10.1086/511070. S2CID 120821801.
  30. ^ "* gam02 And". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved August 19, 2008.
  31. ^ Giridhar, Sunetra; Arellano Ferro, A. (November 2005). "Chemical composition of evolved stars of high galactic latitude". Astronomy and Astrophysics. 443 (1): 297–308. arXiv:astro-ph/0509061. Bibcode:2005A&A...443..297G. doi:10.1051/0004-6361:20041495. S2CID 18557538.
  32. ^ Maestre, L. A.; Wright, J. A. (1960). "A Preliminary Study of the Spectroscopic Binary Gamma Andromedae B". The Astrophysical Journal. 131: 119. Bibcode:1960ApJ...131..119M. doi:10.1086/146813.
  33. ^ "Observation Gamma andromedae AB (9,6") +BC (0,16") - Double Star Observing - Cloudy Nights".

External links[edit]