Gamma Arietis

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Gamma Arietis
Diagram showing star positions and boundaries of the Aries constellation and its surroundings
Cercle rouge 100%.svg

Location of γ Arietis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension 01h 53m 31.81479s[1]
Declination +19° 17′ 37.8790″[1]
Apparent magnitude (V) 3.86 (4.58/4.64)[2]
Spectral type B9 V + A1p Si[2]
U−B color index –0.12[3]
B−V color index –0.04[3]
Radial velocity (Rv) +3.7[4] km/s
Proper motion (μ) RA: +79.20[1] mas/yr
Dec.: –97.63[1] mas/yr
Parallax (π) 19.88 ± 0.96[1] mas
Distance 164 ± 8 ly
(50 ± 2 pc)
Gam1 Ari
Radius 1.9[5] R
Rotational velocity (v sin i) 54[6] km/s
Gam2 Ari
Surface gravity (log g) 4.25[7] cgs
Temperature 10,970[7] K
Metallicity [Fe/H] 0.43 ± 0.14[8] dex
Rotational velocity (v sin i) 201[6] km/s
Other designations
5 Ari, BD+18 243, HIP 8832.[9]
Gam1 Ari: HD 11502, HR 545, SAO 92680.
Gam2 Ari: HD 11503, HR 546, SAO 92681.
Database references
γ1 Ari
γ2 Ari

Gamma Arietis (γ Arietis, abbreviated Gamma Ari, γ Ari) is a binary star in the northern constellation of Aries. The two components are designated γ¹ Arietis and γ² Arietis, also named Mesarthim.[10] The combined apparent visual magnitude of the two stars is 3.86,[2] which is readily visible to the naked eye and makes this the fourth-brightest member of Aries. Based upon an annual parallax shift of 19.88 milliarcseconds,[1] the distance to Gamma Arietis from the Sun is approximately 164 light-years (50 parsecs).


The double star nature of this system was discovered by Robert Hooke in 1664.[11] The two components have an angular separation of 7.606 arcseconds,[2] which can be resolved with a small telescope. The orbital period of the pair is greater than 5000 years.[12] The brighter component, γ² Arietis, is a Lambda Boötis[7] (chemically peculiar) star with a stellar classification of A1p Si and a magnitude of 4.64.[2] It is classified as an α2 CVn type variable star and its brightness varies by 0.04 magnitudes with a period of 2.61 days. The secondary, γ¹ Arietis, is a magnitude 4.58 B-type main-sequence star with a stellar classification of B9 V.[2]


γ Arietis (Latinised to Gamma Arietis) is the system's Bayer designation; γ¹ and γ² Arietis those of its two components.

Gamma Arietis bore the traditional name Mesarthim, of obscure origin, and has been called "the First Star in Aries" as having been at one time the nearest visible star to the equinoctial point. The name Mesarthim may be from the Hebrew word mᵋshārᵋtīm, meaning "the minister",[13] or the Arabic word ألمثرتم Al Muthartim, meaning "the ram".[14] The meaning "servants" has also been suggested.[15] In Sanskrit, Aries is known as Mesha 'The ram' and the First point of Aries (the location of the vernal equinox) is Meshadi. The name could have very well originated from this and transformed to Mesarthim.

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] to catalogue and standardize proper names for stars. The WGSN approved the name Mesarthim for γ² Arietis on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[10]

In Chinese, 婁宿 (Lóusù), meaning Bond (asterism), refers to an asterism consisting of Gamma Arietis, Beta Arietis and Alpha Arietis.[17] Consequently, Gamma Arietis itself is known as 婁宿二 (Lóusù Èr, English: the Second Star of Bond.)[18]

In Hindu astrology, Gamma Arieties and Beta Arietis (Sheratan) are Ashvins, the twin Rigvedic deities who act as doctors of the divine of the world.(Richard H Allen)


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d e f Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, Bibcode:2008MNRAS.389..869E, arXiv:0806.2878Freely accessible, doi:10.1111/j.1365-2966.2008.13596.x. 
  3. ^ a b Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N. 
  4. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W. 
  5. ^ Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy and Astrophysics, 367: 521–524, Bibcode:2001A&A...367..521P, arXiv:astro-ph/0012289Freely accessible, doi:10.1051/0004-6361:20000451. 
  6. ^ a b Royer, F.; et al. (October 2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897–911, Bibcode:2002A&A...393..897R, arXiv:astro-ph/0205255Freely accessible, doi:10.1051/0004-6361:20020943. 
  7. ^ a b c Gerbaldi, M.; Faraggiana, R.; Lai, O. (December 2003), "The heterogeneous class of lambda Bootis stars", Astronomy and Astrophysics, 412: 447–464, Bibcode:2003A&A...412..447G, doi:10.1051/0004-6361:20031472. 
  8. ^ Wu, Yue; et al. (January 2011), "Coudé-feed stellar spectral library - atmospheric parameters", Astronomy and Astrophysics, 525: A71, Bibcode:2011A&A...525A..71W, arXiv:1009.1491Freely accessible, doi:10.1051/0004-6361/201015014. 
  9. ^ "gam Ari -- Variable Star of alpha2 CVn type", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-08-04. 
  10. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  11. ^ Aitken, Robert G. (1935), The Binary Stars, New York: McGraw-Hill, p. 1 
  12. ^ Kaler, James B., "Mesarthim", Stars, University of Illinois, retrieved 2012-08-04. 
  13. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 82, ISBN 0-486-21079-0, retrieved 2010-12-12 
  14. ^ Davis Jr., G. A. (October 1944), "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names", Popular Astronomy, LII (3): 13, Bibcode:1944PA.....52....8D 
  15. ^ "Star names from the National Astronomy and Ionosphere Center". Retrieved 18 October 2012. 
  16. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  17. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  18. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived January 30, 2011, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.

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