Beta Arietis

Beta Arietis (β Arietis, abbreviated Beta Ari, β Ari), officially named Sheratan /ˈʃɛrətæn/,[12][13] is a star system and the second-brightest star in the constellation of Aries, marking the ram's second horn.

β Arietis
Location of β Arietis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension 01h 54m 38.41099s[1]
Declination +20° 48′ 28.9133″[1]
Apparent magnitude (V) 2.655[2]
Characteristics
Spectral type A5 V[3]
U−B color index +0.170[2]
B−V color index +0.142[2]
Astrometry
Radial velocity (Rv)-1.9[4] km/s
Proper motion (μ) RA: +98.74[1] mas/yr
Dec.: -110.41[1] mas/yr
Parallax (π)54.74 ± 0.75 mas[1]
Distance59.6 ± 0.8 ly
(18.3 ± 0.3 pc)
Absolute magnitude (MV)1.55 ± 0.09[5]
Orbit[6]
CompanionBeta Arietis B
Period (P)106.9954 ± 0.0005 days
Semi-major axis (a)36.1 ± 0.3 mas
Eccentricity (e)0.903 ± 0.012
Inclination (i)44.7 ± 1.3°
Longitude of the node (Ω)79.1 ± 0.8°
Argument of periastron (ω)
(secondary)		209.1 ± 1.2°
Details
A
Mass2.34 ± 0.10[6] M☉
Luminosity23[6] L☉
Surface gravity (log g)4.0[7] cgs
Temperature9,000[7] K
Metallicity [Fe/H]0.16[7] dex
Rotational velocity (v sin i)73[8] km/s
Age0.3[9] Gyr
B
Mass1.34 ± 0.07[6] M☉
Luminosity1.3[6] L☉
Other designations
Sheratan, Sharatan, Al Sharatain,[10] 6 Arietis, Gl 80, HR 553, BD +20°306, HD 11636, SAO 75012, FK5 66, HIP 8903.[11]
Database references
SIMBADdata
ARICNSdata

Nomenclature

Beta Arietis is the star's Bayer designation. It also bears the Flamsteed designation 6 Arietis.

The traditional name, Sheratan (or Sharatan, Sheratim),[10] in full Al Sharatan, is from the Arabic الشرطان aš-šaraţān "the two signs", a reference to the star having marked the northern vernal equinox together with Gamma Arietis several thousand years ago. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN approved the name Sheratan for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[13]

In Chinese, 婁宿 (Lóu Xiù), meaning Bond (asterism), refers to an asterism consisting of β Arietis, γ Arietis and α Arietis.[15] Consequently, the Chinese name for β Arietis itself is 婁宿一 (Lóu Su yī, English: the First Star of Bond).[16]

Properties

Beta Arietis has an apparent visual magnitude of 2.66. Based on parallax measurements, it is located at a distance of 59.6 light-years (18.3 parsecs) from Earth. This is a spectroscopic binary star system consisting of a pair of stars orbiting around each other with a separation that can not currently be resolved with a conventional telescope. However, the pair have been resolved using the Mark III Stellar Interferometer at the Mount Wilson Observatory. This allows the orbital elements to be computed, as well as the individual masses of the two stars. The stars complete their highly elliptical orbit every 107 days.[6]

The primary star has a stellar classification of A5 V, which means it is an A-type main-sequence star that is generating energy through the thermonuclear fusion of hydrogen in its core region.[3] The NStars project gives the star a spectral type of kA4 hA5 mA5 Va under the revised MK spectral classification system.[9] The spectrum of the secondary star has not been determined, but, based on the mass, it may have a stellar classification of F5 III–V or G0 V. It is about four magnitudes fainter than the primary; hence the energy output from the system is dominated by the primary star.[6] In a few million years, as the primary evolves toward a red giant, significant amounts of mass transfer to the secondary component is expected.[17]

The primary has been classified as a rapid rotator, with a projected rotational velocity of 73 km/s providing a lower bound on the azimuthal rotational velocity along the equator.[8] It may also be a mildly Am star, which is a class of stars that show a peculiar spectrum with strong absorption lines from various elements and deficiencies in others. In β Arietis, these absorption lines are broadened because of the Doppler effect from the rotation, making analysis of the abundance patterns difficult.[7]

This system has been examined with the Spitzer Space Telescope for the presence of an excess emission of infrared, which would indicate a disk of dust. However, no significant excess was detected.[9]

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. Gutierrez-Moreno, Adelina; et al. (1966). "A System of photometric standards". Publications of the Department of Astronomy University of Chile. Publicaciones Universidad de Chile, Department de Astronomy. 1: 1–17. Bibcode:1966PDAUC...1....1G.
  3. Trilling, D. E.; et al. (April 2007), "Debris disks in main-sequence binary systems", The Astrophysical Journal, 658 (2): 1264–1288, arXiv:astro-ph/0612029, Bibcode:2007ApJ...658.1289T, doi:10.1086/511668, S2CID 14867168
  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. Malkov, O. Yu. (December 2007), "Mass-luminosity relation of intermediate-mass stars", Monthly Notices of the Royal Astronomical Society, 382 (3): 1073–1086, Bibcode:2007MNRAS.382.1073M, doi:10.1111/j.1365-2966.2007.12086.x
  6. Pan, X. P.; et al. (1990), "Apparent orbit of the spectroscopic binary Beta Arietis with the time Mark III Stellar Interferometer", Astrophysical Journal, 356: 641–645, Bibcode:1990ApJ...356..641P, doi:10.1086/168870
  7. Mitton, J. (January 1977), "Spectroscopic observations and curve-of-growth analyses of the four A stars omicron Peg, beta Ari, kappa Ari and 32 Vir.", Astronomy and Astrophysics Supplement Series, 27: 35–46, Bibcode:1977A&AS...27...35M
  8. Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224, S2CID 18475298
  9. Gray, R. O.; et al. (October 2003), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.", The Astronomical Journal, 126 (4): 2048–2059, arXiv:astro-ph/0308182, Bibcode:2003AJ....126.2048G, doi:10.1086/378365, S2CID 119417105
  10. Allen, Richard Hinckley (1899), Star-Names and Their Meanings, New York: G. E. Stechert, pp. 81–82, retrieved 2011-12-24
  11. "bet Ari -- Spectroscopic binary", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-29
  12. 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.
  13. "IAU Catalog of Star Names". Retrieved 28 July 2016.
  14. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  15. (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.
  16. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-08-18 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. Fuhrmann, Klaus (February 2008), "Nearby stars of the Galactic disc and halo - IV", Monthly Notices of the Royal Astronomical Society, 384 (1): 173–224, Bibcode:2008MNRAS.384..173F, doi:10.1111/j.1365-2966.2007.12671.x
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