Gamma Andromedae

Almach

The star system (not scaled)

Gamma Andromedae (γ Andromedae, abbreviated Gamma And, γ And) is the third-brightest point of light in the constellation of Andromeda.

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, also named Almach^[1]) next to a dimmer, indigo-blue star (γ² Andromedae), separated by approximately 10 arcseconds. It is often considered by stargazers to be a beautiful double star with a striking contrast of color.^[2][3][4] 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, approximately 350 light-years from the Earth.^[2][5]

Nomenclature

• Gamma Andromedae is the star's Bayer designation.
• In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[6] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016^[7] included a table of the first two batches of names approved by the WGSN, which included Almach for γ1 Andromedae.
• Almach was the traditional name (also spelt as Almaach, Almaack, Almak, Almaak, or Alamak), derived from the Arabic العناق الأرض al-‘anāq al-’arđ̧^[8] "the caracal" (desert lynx).^[9]
• Another term for this star used by medieval astronomers writing in Arabic was آلرجل المسلسلة Al Rijl al Musalsalah "the Woman's Foot"^[8]
• 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, γ Andromedae itself is known as 天大將軍一 (Tiān Dà Jiāng Jūn yī, English: the First Star of Heaven's Great General.).^[10]
• 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.^[11][12]
• In the Babylonian star catalogues, γ Andromedae together with Triangulum formed the constellation known as ^MULAPIN (𒀯𒀳) "The Plough".^[13]
• Astrologically this star was considered "honourable and eminent."^[14]

Stellar properties

γ¹ Andromedae
(γ Andromedae A)

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Andromeda
Right ascension	02^h 03^m 53.9531^s[3]
Declination	+42° 19′ 47.009″[3]
Apparent magnitude (V)	2.26[3]
Characteristics
Spectral type	K3IIb[15]
U−B color index	+1.58[15]
B−V color index	+1.37[15]
R−I color index	+0.68[15]
Astrometry
Radial velocity (Rv)	−11.7 ± 0.9[3] 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
Distance	350 ± 30 ly (109 ± 9 pc)
Absolute magnitude (MV)	−2.9[16]
Details
Radius	80[17] R☉
Luminosity	2,000[17] L☉
Temperature	4,500[17] K
Rotational velocity (v sin i)	< 17[15] km/s
Other designations
Almach, Almaach, Almak, Almaak, Alamak, γ^1 And, Gamma^1 Andromedae, Gamma^1 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][15][18]
Database references
SIMBAD	data

Relative sizes of the components to the Sun (top right). Circle sizes relate to solar radii, italic numbers are solar mass estimates to 4SF. Sizes of BA, BB, and C are estimates.

γ¹ Andromedae is a bright giant star with a spectral classification of K3IIb. It has an apparent visual magnitude of approximately 2.26.^[15]

γ² Andromedae
(γ Andromedae BC)

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Andromeda
Right ascension	02^h 03^m 54.720^s (B)[19]
Declination	+42° 19′ 51.41″ (B)[19]
Apparent magnitude (V)	4.84 (BC)      (combined) 5.5 (B) 6.3 (C)[20]
Characteristics
Spectral type	B9.5V/B9.5V (B)    (spectroscopic binary)[21] A0V (C)[22]
U−B color index	−0.12[20]
B−V color index	+0.03[20]
Astrometry
Radial velocity (Rv)	−14 ± 5 (B)[4] km/s
Proper motion (μ)	RA: 37 (B)[4] mas/yr Dec.: −57 (B)[4] mas/yr
Parallax (π)	9.19 ± 0.73[19] mas
Distance	350 ± 30 ly (109 ± 9 pc)
Absolute magnitude (MV)	−0.3 (BC)[16]
Orbit[23]
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) (secondary)	183.4 ± 15.0°
Position (relative to γ^1 And)
Epoch of observation	2004
Angular distance	9.6″ [18]
Position angle	63° [18]
Other designations
γ^2 And, Gamma^2 Andromedae, Gamma^2 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.[4][18][24]
Database references
SIMBAD	data

γ² Andromedae, with an overall apparent visual magnitude of 4.84,^[20] is 9.6 arcseconds away from γ¹ Andromedae at a position angle of 63 degrees.^[18]

In October 1842, Wilhelm Struve found that γ² Andromedae was itself a double star whose components were separated by less than an arcsecond.^[8] 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.^[20] They have an orbital period of about 64 years.^[23] 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.^[21]

Location

The star's location is shown in the following chart of the Andromeda constellation:

Andromeda Constellation

Almach as a name

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

See also

• Gamma Andromedae in fiction
• NGC 752

References

1. "IAU Catalog of Star Names". Retrieved 28 July 2016.
2. pp. 113–114, vol. 1, Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Robert Burnham, New York: Courier Dover Publications, 1978, ISBN 0-486-23567-X.
3. NAME ALMACH -- Star in double system, database entry, SIMBAD. Accessed on line August 19, 2008.
4. HD 12534 -- Spectroscopic binary, database entry, SIMBAD. Accessed on line August 19, 2008.
5. 01578+4151, database entry, MSC - a catalogue of physical multiple stars, A. A. Tokovinin, CDS database ID J/A+AS/124/75.
6. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
7. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
8. p. 36–37, Star-names and Their Meanings, Richard Hinckley Allen, New York: G. E. Stechert, 1899.
9. p. 23, Star tales, Ian Ridpath, James Clarke & Co., 1989, ISBN 0-7188-2695-7.
10. (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 10 日
11. 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: 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
12. 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 See Star Name - R.H.Allen p. 160. In Al Achsasi Al Mouakket catalogue, η Cet as Aoul al Naamat or Prima Struthionum (the first ostrich), θ Cet as Thanih al Naamat or Secunda Struthionum (the second ostrich), τ Cet as Thalath al Naamat or Tertia Struthionum (the third ostrich), and ζ Cet as Rabah al Naamat or Quarta Struthionum (the fourth ostrich). υ Cet should be Khamis al Naamat or Quinta Struthionum (the fifth ostrich) consistently, but Al Achsasi Al Mouakket designated the title the fifth ostrich to γ Gam with uncleared consideration.
13. Origins of the ancient constellations: I. The Mesopotamian traditions, J. H. Rogers, Journal of the British Astronomical Association 108, #1 (February 1998), pp. 9–28, Bibcode: 1998JBAA..108....9R.
14. p.27, Star Lore of All Ages, William Tyler Olcott, G.P. Putnam's Sons, New York and London, The Knickerbocker Press, 1911
15. HR 603, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line August 19, 2008.
16. From apparent magnitude and parallax.
17. Almach, Jim Kaler, Stars. Accessed on line August 19, 2008.
18. Entry 02039+4220, discoverer code STF 205, components A-BC, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line August 27, 2008.
19. Component 2, HIP 9640, database entry, Hipparcos catalogue, CDS ID I/239.
20. HR 604, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line August 19, 2008.
21. A Preliminary Study of the Spectroscopic Binary Gamma Andromedae B, L. A. Maestre and J. A. Wright, Astrophysical Journal 131 (January 1960), pp. 119–121, Bibcode: 1960ApJ...131..119M.
22. Entry 02039+4220, discoverer code STT  38BC, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line August 19, 2008.
23. Entry 02039+4220, Sixth Catalog of Orbits of Visual Binary Stars, William I. Hartkopf & Brian D. Mason, United States Naval Observatory. Accessed on line August 21, 2007.
24. BD+41 395C -- Star in double system, database entry, SIMBAD. Accessed on line August 21, 2008.

External links

• Almaak (Gamma Andromedae) at The Internet Encyclopedia of Science
• Image ALMACH
• Almaak on AstroDwarf
• Gamma Andromedae on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

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