Omega Herculis

Omega Herculis (ω Herculis, abbreviated Ome Her, ω Her) is a binary star[2] system in the northern constellation of Hercules. Based upon an annual parallax shift of 13.04 mas as seen from Earth, it is located around 250 light-years from the Sun. It is faintly visible to the naked eye, having a combined apparent visual magnitude of 4.58.[1] The system is a candidate for membership in the Ursa Major Moving Group, although this remains uncertain.[7]

Omega Herculis

Historical view of the Hercules constellation showing the star Kajam (ω Her) as "the club" in the hero's right hand.
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hercules
Right ascension 16h 25m 24.95425s[1]
Declination +14° 01′ 59.7711″[1]
Apparent magnitude (V) 4.5821[1] (4.58 + 11.5)[2]
Characteristics
Spectral type A2 Vp CrSr[3]
U−B color index +0.01[4]
B−V color index +0.00[4]
Variable type α2 CVn[5]
Astrometry
Radial velocity (Rv)−5.90±0.74[6] km/s
Proper motion (μ) RA: +40.86[1] mas/yr
Dec.: −59.71[1] mas/yr
Parallax (π)13.04 ± 0.64[1] mas
Distance250 ± 10 ly
(77 ± 4 pc)
Absolute magnitude (MV)0.29±0.15[7]
Details
ω Her A
Mass2.14[8] M☉
Radius3.30[9] R☉
Luminosity70[10] L☉
Surface gravity (log g)3.51±0.35[11] cgs
Temperature10,052±320[11] K
Metallicity [Fe/H]+0.47±0.15[11] dex
Rotation2.951[12] d
Rotational velocity (v sin i)55[13] km/s
Age149[8] Myr
Other designations
Cujam, ω Her, 24 Her, BD+14° 3049, FK5 613, HD 148112, HIP 80463, HR 6117, SAO 102153, WDS J16254+1402AB.[14]
Database references
SIMBADdata

The two components are designated Omega Herculis A (officially named Cujam /ˈkjuːdʒəm/, the traditional name of the system)[15] and B.

Nomenclature

ω Herculis (Latinised to Omega Herculis) is the system's Bayer designation. It previously bore the Flamsteed designation of 51 Serpentis before being added to Hercules.[16] The designations of the two components as Omega Herculis 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).[17]

The system bore the traditional name Cujam (also written as Cajam and Kajam), meaning ("club").[18] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[19][20] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[21] It approved the name Cujam for the component Omega Herculis A on February 1, 2017 and it is now so included in the List of IAU-approved Star Names.[15]

In Chinese, 斗 (Dǒu), meaning Dipper for Liquid, refers to an asterism consisting of Omega Herculis, 49 Serpentis, 13 Herculis, 29 Herculis and 33 Herculis.[22] Consequently, the Chinese name for Omega Herculis itself is 斗一 (Dǒu yī, English: the First Star of Dipper for Liquid).[23]

Properties

The primary, Omega Herculis A, is a chemically peculiar Ap star with a stellar classification of A2 Vp CrSr.[3] The spectrum displays abnormally strong absorption lines of chromium and strontium, and weak lines of calcium and magnesium.[3] An A-type star, it has an estimated 2.14[8] times the mass of the Sun and 3.30[9] times the Sun's radius. The star is around 149[8] million years old and is radiating 70[10] times the solar luminosity from its photosphere at an effective temperature of 10,052 K.[11]

This component is an Alpha2 Canum Venaticorum variable[5] with a brightness amplitude of 0.4 magnitude and a 2.951 day phase that presumably matches the rotation period. The pattern of variation shows that there are regions of the star's surface where the concentrations of elements differ. The star also displays short period variations on the order of 2.5 hours.[12] It has a mean effective magnetic field value of 209×10−4 T.[24]

The secondary, Omega Herculis B, is a magnitude 11.5 companion star.[2] As of 2010, it was located at an angular separation of 0.80 arc seconds along a position angle of 294°.[25]

References
  1. van Leeuwen, F. (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. (July 1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.
  4. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  5. Dubath, P.; et al. (2011), "Random forest automated supervised classification of Hipparcos periodic variable stars", Monthly Notices of the Royal Astronomical Society, 414 (3): 2602–17, arXiv:1101.2406, Bibcode:2011MNRAS.414.2602D, doi:10.1111/j.1365-2966.2011.18575.x, S2CID 118560311.
  6. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  7. King, Jeremy R.; et al. (April 2003), "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group", The Astronomical Journal, 125 (4): 1980–2017, Bibcode:2003AJ....125.1980K, doi:10.1086/368241.
  8. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
  9. Shulyak, D.; et al. (2014), "Interferometry of chemically peculiar stars: Theoretical predictions versus modern observing facilities", Monthly Notices of the Royal Astronomical Society, 443 (2): 1629, arXiv:1406.6093, Bibcode:2014MNRAS.443.1629S, doi:10.1093/mnras/stu1259, S2CID 96452769.
  10. McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
  11. Prugniel, Ph.; et al. (2011), "The atmospheric parameters and spectral interpolator for the MILES stars", Astronomy & Astrophysics, 531: A165, arXiv:1104.4952, Bibcode:2011A&A...531A.165P, doi:10.1051/0004-6361/201116769, S2CID 54940439.
  12. Aslanov, I. A. (August 1987), "Spectral Variable Star HD148112 - Spectrophotometry of Lines", Soviet Astronomy, 31 (4): 425, Bibcode:1987SvA....31..425A.
  13. Abt, Helmut A.; et al. (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590.
  14. "ome Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-03-31.
  15. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  16. Wagman, M. (August 1987), "Flamsteed's Missing Stars", Journal for the History of Astronomy, 18 (3): 209–223, Bibcode:1987JHA....18..209W, doi:10.1177/002182868701800305, S2CID 118445625.
  17. 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].
  18. Kaler, James B. (August 22, 2013), "Cujam", Stars, University of Illinois, retrieved 2016-05-13.
  19. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  20. IAU Formally Approves 227 Star Names, International Astronomical Union, retrieved 24 November 2016.
  21. "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  22. (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.
  23. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2009-09-29 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  24. Glagolevskij, Yu. V. (September 2007), "Magnetic-field dependence of chemical anomalies in CP stars", Astrophysical Bulletin, 62 (3): 244–256, Bibcode:2007AstBu..62..244G, doi:10.1134/S1990341307030054, S2CID 122706004.
  25. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.

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