Sigma2_Ursae_Majoris

Sigma<sup>2</sup> Ursae Majoris

Sigma2 Ursae Majoris

Binary star in the constellation Ursa Major

Sigma2 Ursae Majoris (σ2 Ursae Majoris, σ2 UMa) is a binary star in the constellation of Ursa Major. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 66.5 light years (20.4 parsecs) from Earth, making this a fairly nearby system. The primary component has an apparent magnitude of about 4.8,[1] meaning it can be seen with the naked eye (see Bortle scale).

For other stars with this Bayer designation, see σ Ursae Majoris.
Quick Facts Apparent magnitude (V), Characteristics ...

This is a visual binary, meaning that the two components can be resolved, and the orbit is derived from the positions of the two stars. The primary component Sigma2 Ursae Majoris A, is a white-colored F-type subgiant. Its radius is about 1.75 times that of the Sun, and it is 31% more massive.[7] The companion is an orange K-type main-sequence star that is much fainter. The two stars are separated about 4 arcseconds away, and because of their slow orbital motion the orbit is poorly known: estimates of the orbital period range from 970 years[8] to over 1,500 years.[9] There is a third component, designated Sigma2 Ursae Majoris C. Located 205 arcseconds from the primary, it is thought to be a line-of-sight coincidence, and is not related to the system.

Naming

  • With π1, π2, σ1, ρ, A and d, it composed the Arabic asterism الظِّبَاء aẓ-Ẓibāʾ meaning the Gazelles.[10] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Ṭhibā were the title for seven stars : A as Althiba I, π1 as Althiba II, π2 as Althiba III, ρ as Althiba IV, σ1 as Althiba V, this star (σ2) as Althiba VI, and d as Althiba VII.[11]
  • In Chinese, 三師 (Sān Shī), meaning Three Top Instructors, refers to an asterism consisting of σ2 Ursae Majoris and ρ Ursae Majoris. Consequently, σ2 Ursae Majoris itself is known as 三師三 (Sān Shī sān, English: the Third Star of Three Top Instructors.).[12]

References

  1. [1]
    Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  2. [2]
    Edwards, T. W. (1976). "MK classification for visual binary components". Astronomical Journal. 81: 245–249. Bibcode:1976AJ.....81..245E. doi:10.1086/111879.
  3. [3]
    Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  4. [4]
    "* sig02 UMa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 27 March 2017.
  5. [5]
    de Medeiros, J. R.; Mayor, M. (1999). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement. 139 (3): 433–460. arXiv:astro-ph/0608248. Bibcode:1999A&AS..139..433D. doi:10.1051/aas:1999401.
  6. [6]
    van Leeuwen, F.; et al. (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.
  7. [7]
    Fuhrmann, Klaus (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.
  8. [8]
    "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 2017-08-01. Retrieved 2017-04-01.
  9. [9]
    Shklovskii, I. S.; Wenzel, W. (1980). "Book-Review - Stars Their Birth Life and Death". Astronomische Nachrichten. 301: 99. Bibcode:1980AN....301...99S. doi:10.1002/asna.2103010207.
  10. [10]
    Allen, Richard Hinckley (1899), Star-Names and Their Meanings, New York: G. E. Stechert, p. 444
  11. [11]
    Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology.
  12. [12]
    (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 16 日
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