Gamma Arietis

Gamma Arietis (γ Arietis, abbreviated Gamma Ari, γ Ari) is a binary star (possibly trinary) 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). γ1 Arietis may itself be a spectroscopic binary with a low mass companion.

γ Arietis
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]
Characteristics
Gamma1 Ari (B)
Spectral type A0Vnp λ Boo[3] (A0IV-V(n)kB8)[4]
B−V color index −0.14[4]
Gamma2 Ari (A)
Spectral type A2IVpSiSrCr[5]
B−V color index −0.03[4]
Variable type α2 CVn[6]
Astrometry
Radial velocity (Rv)+3.7[7] km/s
Proper motion (μ) RA: +79.20[1] mas/yr
Dec.: −97.63[1] mas/yr
Parallax (π)19.88 ± 0.96 mas[1]
Distance164 ± 8 ly
(50 ± 2 pc)
Details
Gamma1 Ari (Ba)
Mass2.67[8] M☉
Radius2.014 R☉
Luminosity42.0 L☉
Surface gravity (log g)4.26[8] cgs
Temperature10,356[8] K
Rotational velocity (v sin i)54[9] km/s
Age34[10] Myr
Gamma2 Ari (A)
Mass2.72[8] M☉
Radius1.941[8] R☉
Luminosity41.5 L☉
Surface gravity (log g)4.30[8] cgs
Temperature10,512[8] K
Metallicity [Fe/H]0.43±0.14[11] dex
Rotational velocity (v sin i)201[9] km/s
Gamma1 Ari (Bb)
Mass0.7[10] M☉
Temperature4,312[10] K
Metallicity [Fe/H]−0.5[10] dex
Rotational velocity (v sin i)5[10] km/s
Other designations
5 Ari, BD+18 243, HIP 8832, WDS J01535+1918[12]
Gamma1 Ari (B): HD 11502, HR 545, SAO 92680, WDS J01535+1918B.
Gamma2 Ari (A): HD 11503, HR 546, SAO 92681, WDS J01535+1918A
Database references
SIMBADγ Ari
γ1 Ari (B)
γ2 Ari (A)

The combined apparent visual magnitude of the 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).

Properties

The double star nature of this system was discovered by Robert Hooke in 1664.[13] 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.[14]

A light curve for Gamma Arietis, plotted from TESS data,[15] folded with a period of 1.6092 days[16]

The brighter component, γ2 Arietis, is an α2 CVn type variable star, a type of star with a strong magnetic field and enhanced spectral lines of some metals, with high chromospheric activity causing brightness changes as the star rotates. Its brightness varies by 0.04 magnitudes with a period of 2.61 days.[6] It is also an Ap star, a type of chemically peculiar star with enhanced lines of many metals.[17] The spectral class has been given as A2IVpSiSrCr, noting the particular strength of lines of silicon, strontium, and chromium, although other lines such as europium, mercury, and manganese are also stronger than in a normal star. This spectral type suggests that the star is an A2-class subgiant.[18] One study identified a low-mass companion to γ2 Arietis, a probable red dwarf in a close orbit.[10]

The marginally fainter of the two visible stars, γ1 Arietis, is a Lambda Boötis[19] (chemically peculiar) star with a stellar classification of A0Vnp and a magnitude of 4.64.[3] Lambda Boötis stars are identified based on unusually low abundances of iron peak elements in their spectra. The spectral class has also been given as A0IV-V(n)kB8, indicating that calcium K lines in its spectrum are more typical of a B8 star.[4] Older studies often classified it as B9 or B9.5 with a luminosity class of IV or V, indicating either a main sequence or subgiant.[18]

Both of the visible stars have mass of about 2.7 M☉, luminosities of about 40 L☉, effective temperatures of about 10,000 K, and radii of about 2 R☉. Their age is about 34 million years.

Nomenclature

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).[20]

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.[21]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[22] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[23] 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.[24]

In Chinese, 婁宿 (Lóusù), meaning Bond (asterism), refers to an asterism consisting of Gamma, Beta and Alpha Arietis.[25] Consequently, the Chinese name for Gamma Arietis itself is 婁宿二 (Lóusù Èr, English: the Second Star of Bond).[26]

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)

References
  1. 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. 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. Abt, Helmut A.; Morrell, Nidia I. (1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", The Astrophysical Journal Supplement Series, 99: 135–172, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.
  4. Murphy, Simon J.; et al. (October 2015), "An Evaluation of the Membership Probability of 212 λ Boo Stars. I. A Catalogue", Publications of the Astronomical Society of Australia, 32: 43, arXiv:1508.03633, Bibcode:2015PASA...32...36M, doi:10.1017/pasa.2015.34, S2CID 59405545, e036.
  5. Abt, H. A.; Cardona, O. (January 1, 1984), "The nature of the visual companions of Ap and Am stars", Astrophysical Journal, Part 1, 276: 266–269, Bibcode:1984ApJ...276..266A, doi:10.1086/161610.
  6. Samus', N. N; et al. (2017), "General catalogue of variable stars", Astronomy Reports, GCVS 5.1, 61 (1): 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  7. 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.
  8. Stassun, Keivan G.; et al. (2019-10-01), "The Revised TESS Input Catalog and Candidate Target List", The Astronomical Journal, 158 (4): 138, arXiv:1905.10694, Bibcode:2019AJ....158..138S, doi:10.3847/1538-3881/ab3467, hdl:1721.1/124721, ISSN 0004-6256, S2CID 166227927.
  9. 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.
  10. Gullikson, Kevin; et al. (August 2016), "The Close Companion Mass-ratio Distribution of Intermediate-mass Stars", The Astronomical Journal, 152 (2): 13, arXiv:1604.06456, Bibcode:2016AJ....152...40G, doi:10.3847/0004-6256/152/2/40, S2CID 119179065, 40.
  11. 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.
  12. "gam Ari", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2012-08-04.
  13. Aitken, Robert G. (1935), The Binary Stars, New York: McGraw-Hill, p. 1.
  14. Kaler, James B., "Mesarthim", Stars, University of Illinois, retrieved 2012-08-04.
  15. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  16. "gam Ari". The International Variable Star Index. AAVSO. Retrieved 3 July 2022.
  17. Renson, P.; Manfroid, J. (May 2009), "Catalogue of Ap, HgMn and Am stars", Astronomy and Astrophysics, 498 (3): 961–966, Bibcode:2009A&A...498..961R, doi:10.1051/0004-6361/200810788.
  18. Skiff, B. A. (2014), "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009-2016)", VizieR On-line Data Catalog: B/Mk. Originally Published in: Lowell Observatory (October 2014), 1, Bibcode:2014yCat....1.2023S.
  19. 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.
  20. 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.
  21. 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.
  22. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  23. WG Triennial Report (2015-2018) - Star Names (PDF), p. 5, retrieved 2018-07-14.
  24. IAU Catalog of Star Names, retrieved 28 July 2016.
  25. (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.
  26. (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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