Gamma Arietis

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γ Arietis
Aries constellation map.svg
Red circle.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
Distance164 ± 8 ly
(50 ± 2 pc)
Gam¹ Ari
Radius1.9[5] R
Rotational velocity (v sin i)54[6] km/s
Gam² Ari
Surface gravity (log g)4.25[7] cgs
Temperature10,970[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, WDS J01535+1918AB.[9]
Gam¹ Ari: HD 11502, HR 545, SAO 92680, WDS J01535+1918B.
Gam² Ari: HD 11503, HR 546, SAO 92681, WDS J01535+1918A.
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 or Gamma Arietis B and γ² Arietis or Gamma Arietis A (formally named Mesarthim /mɛˈsɑːrθɪm/, the traditional name for the Gamma Arietis system).[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 parallax measurements obtained during the Hipparcos mission,[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. The designation of the two components as Gamma Arietis 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).[13]

Gamma Arietis has been called "the First Star in Aries" as having been at one time the nearest visible star to the equinoctial point.

It bore the traditional name Mesarthim. Originally it had shared the name Sheratan with Beta Arietis. However, this got corrupted to "Sartai" in medieval manuscripts, which Bayer erroneously explained as being the Hebrew grammatical term מְשָׁרְתִים mᵉshārᵉthīm "servants", and later scholars picked up on this term.[14]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[16] It approved the name Mesarthim for the component 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, Beta and Alpha Arietis.[17] Consequently, the Chinese name for Gamma Arietis itself is 婁宿二 (Lóusù Èr, English: the Second Star of Bond).[18]

In Hindu astrology, Gamma Arietis 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, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
  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, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  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", Carnegie Institute Washington D.C. Publication, 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 (2): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
  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, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943, S2CID 14070763.
  7. ^ a b c Gerbaldi, M.; Faraggiana, R.; Lai, O. (December 2003), "The heterogeneous class of lambda Bootis stars", Astronomy and Astrophysics, 412 (2): 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, arXiv:1009.1491, Bibcode:2011A&A...525A..71W, doi:10.1051/0004-6361/201015014, S2CID 53480665.
  9. ^ "gam Ari". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-08-04.CS1 maint: postscript (link)
  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. ^ 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].
  14. ^ 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.
  15. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  16. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  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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