Gamma Andromedae

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
γ1 Andromedae
(γ Andromedae A)
Andromeda constellation map.svg
Red circle.svg
Location of γ Andromedae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Andromeda
Right ascension 02h 03m 54.0s[1]
Declination +42° 19′ 47″[1]
Apparent magnitude (V) 2.27[1]
Spectral type K3IIb[1]
U−B color index +1.58[1]
B−V color index +1.37[1]
R−I color index +0.68[1]
Radial velocity (Rv)−11.7 ± 0.9[2] km/s
Proper motion (μ) RA: 43.08[3] mas/yr
Dec.: −50.85[3] mas/yr
Parallax (π)9.19 ± 0.73[3] mas
Distance350 ± 30 ly
(109 ± 9 pc)
Radius80[4] R
Luminosity2,000[4] L
Temperature4,500[4] K
Rotational velocity (v sin i)< 17[1] 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, STF 205A, ADS 1630 A, BD+41 395, CCDM J02039+4220A, FK5 73, GC 2477, HD 12533, HIP 9640, HR 603, IDS 01578+4151 A, PPM 44721, SAO 37734, WDS 02039+4220A[3][1][6]
Database references

Gamma Andromedae (γ Andromedae, abbreviated Gamma And, γ And) is the third-brightest point of light in the constellation of Andromeda. It is a multiple star system approximately 350 light-years from the Earth.


An image of γ Andromedae as it appears in a small telescope

In 1778, Johann Tobias Mayer discovered that γ Andromedae was a double star. When examined in a small telescope, it appears to be a bright, golden-yellow star (γ1 Andromedae or γ Andromedae A, officially named Almach /ˈælmæk/, the traditional name for the entire system)[7][8] next to a dimmer, indigo-blue star (γ2 Andromedae or γ Andromedae B), separated by approximately 10 arcseconds. It is often considered by stargazers to be a beautiful double star with a striking contrast of color.[9] 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.[9][10]


Stellar properties[edit]

Components of the γ Andromedae system (not to scale)
γ2 Andromedae
(γ Andromedae BC)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Andromeda
Right ascension 02h 03m 54.720s (B)[20]
Declination +42° 19′ 51.41″ (B)[20]
Apparent magnitude (V) 4.84 (BC combined)

5.5 (B)
6.3 (C)[21]

Spectral type B9.5V/B9.5V (B)

A0V (C)[22]

U−B color index −0.12[21]
B−V color index +0.03[21]
Radial velocity (Rv)−14.0±5[2] km/s
Proper motion (μ) RA: 3730.021[23] mas/yr
Dec.: −51.640[23] mas/yr
Parallax (π)12.5653 ± 0.5881[23] mas
Distance260 ± 10 ly
(80 ± 4 pc)
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)B2015.5 ± 1.5
Argument of periastron (ω)
183.4 ± 15.0°
Position (relative to γ1 And)
Epoch of observation2004
Angular distance9.6 [6]
Position angle63° [6]
Other designations
γ2 And, Gamma2 Andromedae, Gamma2 And, γ Andromedae BC, γ And BC, Gamma Andromedae BC, Gamma And BC, 57 Andromedae BC, 57 And BC, HD 12534, HIP 9640, HR 604, SAO 37735, WDS 02039+4220BC[25][6]
Database references

γ1 Andromedae (A component) is a bright giant star with a spectral classification of K3IIb. It has an apparent visual magnitude of approximately 2.26.[1]

γ2 Andromedae (BC component), with an overall apparent visual magnitude of 4.84,[21] is 9.6 arcseconds away from γ1 Andromedae at a position angle of 63 degrees.[6]

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

In October 1842, Wilhelm Struve found that γ2 Andromedae was itself a double star whose components were separated by less than an arcsecond.[13] The components are an object of apparent visual magnitude 5.5, γ Andromedae B, and a type-A main sequence star with apparent visual magnitude 6.3, γ Andromedae C.[21] They have an orbital period of about 64 years.[24] Spectrograms taken from 1957 to 1959 revealed that γ Andromedae B was itself a spectroscopic binary, composed of two type-B main sequence stars orbiting each other with a period of 2.67 days.[26]

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 f g h i j Hoffleit, Dorrit; Jaschek, Carlos (1991). The Bright star catalogue. "database entry". CDS. Retrieved 2019-11-19.
  2. ^ a b Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
  3. ^ a b c d [‹See Tfd› "* gam01 And"] Check |url= value (help). SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved August 19, 2008.
  4. ^ a b c Jim Kaler. "Almach". Stars. Retrieved 2019-11-19.
  5. ^ a b Tokovinin, A. A. "HIP 9640". Multiple Star Catalogue. Retrieved 2019-11-19.
  6. ^ 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.
  7. ^ 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 Pub. ISBN 978-1-931559-44-7.
  8. ^ a b "Naming Stars". Retrieved 16 December 2017.
  9. ^ a b Robert Burnham (1 January 1978). Andromeda-Cetus. Courier Corporation. ISBN 978-0-486-23567-7.
  10. ^ A. A. Tokovinin. "MSC - a catalogue of physical multiple stars". CDS. Retrieved 2019-11-19.
  11. ^ 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].
  12. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  13. ^ a b c Richard Hinckley Allen (1899). Star-names and Their Meanings. New York: G.E. Stechert. pp. 36–37.
  14. ^ Ridpath, Ian (1988). Star Tales. ISBN 0-7188-2695-7.
  15. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 10 日
  16. ^ 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.
  17. ^ 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.
  18. ^ 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.
  19. ^ William Tyler Olcott (December 1985). Star Lore of All Ages. Health Research Books. ISBN 978-0-7873-1096-7.
  20. ^ a b Component 2, HIP 9640, database entry, Hipparcos catalogue, CDS ID I/239.
  21. ^ a b c d e Hoffleit, Dorrit; Jaschek, Carlos (1991). The Bright star catalogue. "database entry". CDS. Retrieved 2019-11-19.
  22. ^ 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.
  23. ^ 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.
  24. ^ a b Entry 02039+4220, Sixth Catalog of Orbits of Visual Binary Stars Archived 2017-11-12 at the Wayback Machine, William I. Hartkopf & Brian D. Mason, United States Naval Observatory. Accessed on line August 21, 2007.
  25. ^ [‹See Tfd› "* gam02 And"] Check |url= value (help). SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved August 19, 2008.
  26. ^ 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.

External links[edit]

Coordinates: Sky map 02h 03m 53.9531s, +42° 19′ 47.009″