Eta Ophiuchi

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Eta Ophiuchi (Sabik)
Location of η Ophiuchi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension 17h 10m 22.68689s[1]
Declination –15° 43′ 29.6639″[1]
Apparent magnitude (V) 2.43[2] (3.05/3.27)[3]
Spectral type A1 IV + A1 IV[3]
U−B color index +0.09[2]
B−V color index +0.05[2]
Radial velocity (Rv)–0.9[4] km/s
Proper motion (μ) RA: +40.13[1] mas/yr
Dec.: +99.17[1] mas/yr
Parallax (π)36.91 ± 0.80 mas[1]
Distance88 ± 2 ly
(27.1 ± 0.6 pc)
Period (P)87.58 ± 1.00 yr
Semi-major axis (a)1.396 ± 0.010″
Eccentricity (e)0.950 ± 0.020
Inclination (i)95.2 ± 2.0°
Longitude of the node (Ω)38.9 ± 1.0°
Periastron epoch (T)2024.68 ± 0.50
Argument of periastron (ω)
274.8 ± 2.0°
Metallicity [Fe/H]−0.01[5] dex
η Oph A
Mass2.966[3] M
Rotational velocity (v sin i)23[6] km/s
η Oph B
Mass3.478[3] M
Other designations
35 Oph, BD–15°4467, GCTP 3895.00, Gl 656.1A/B, HD 155125, HIP 84012, HR 6378, SAO 160332, WDS J17104-1544AB.
Database references

Eta Ophiuchi (η Ophiuchi, abbreviated Eta Oph, η Oph) is a binary star in the constellation of Ophiuchus. Based on parallax measurements taken during the Hipparcos mission, it is approximately 88 light-years from the Sun.

Eta Ophiuchi is part of a multiple star system designated WDS J17104-1544. It itself is designated WDS J17104-1544AB and its two components WDS J17104-1544A (also called Sabik /ˈsbɪk/, the traditional name for the system)[7][8] and WDS J17104-1544B. The 'C' component is UCAC4 372-080717[9] and 'D' is UCAC2 26022336.[10]


η Ophiuchi (Latinised to Eta Ophiuchi) is the system's Bayer designation. WDS J17104-1544AB is its designation in the Washington Double Star Catalog. The designations of the two components as WDS J17104-1544 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).[11]

It bore the traditional name Sabik, from the Arabic السابق al-sābiq "the preceding one", of uncertain reference.[7] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] to catalogue and standardize proper names for stars. The WGSN approved the name Sabik for the component WDS J17104-1544 A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[8]

In Chinese, this star is considered part of 天市左垣 (Tiān Shì Zuǒ Yuán), meaning Left Wall of Heavenly Market Enclosure, which refers to an asterism representing eleven old states in China that mark the left borderline of the enclosure, consisting of Eta Ophiuchi, Delta Herculis, Lambda Herculis, Mu Herculis, Omicron Herculis, 112 Herculis, Zeta Aquilae, Theta¹ Serpentis, Eta Serpentis, Nu Ophiuchi and Xi Serpentis.[13] Consequently, the Chinese name for Eta Ophiuchi itself is 天市左垣十一 (Tiān Shì Zuǒ Yuán shíyī, English: the Eleventh Star of Left Wall of Heavenly Market Enclosure), representing the state Song (宋).[14][15]


USS Sabik (AK-121) was a United States Navy Crater class cargo ship named after the star.


Eta Ophiuchi is a binary system that is difficult to resolve in amateur telescopes but whose true nature was determined through use of more advanced techniques. The primary star (whose observational data make up the table in this article) is actually only slightly larger and hotter than its companion. Individually each star is a fairly unremarkable A class main sequence star, but as a binary pair they are unusual. Each star orbits around a common center in a close and highly elliptical orbit, making planetary formation unlikely in this system and some stellar data imprecise.[citation needed]


  1. ^ a b c d e 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 Hoffleit, D.; Warren, W. H. Jr. (1991). "Entry for HR 2491". Bright Star Catalogue (5th revised (Preliminary Version) ed.). CDS. ID V/50.
  3. ^ a b c d e Docobo, J. A.; Ling, J. F. (April 2007), "Orbits and System Masses of 14 Visual Double Stars with Early-Type Components", The Astronomical Journal, 133 (4): 1209–1216, Bibcode:2007AJ....133.1209D, doi:10.1086/511070, S2CID 120821801
  4. ^ Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Washington: Carnegie Institution of Washington: 0, Bibcode:1953GCRV..C......0W
  5. ^ Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Bubar, E. J.; McGahee, C. E.; O'Donoghue, A. A.; Knox, E. R. (2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc--The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637. S2CID 119476992.
  6. ^ 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
  7. ^ a b 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.
  8. ^ a b "Naming Stars". Retrieved 27 February 2018.
  9. ^ "UCAC4 372-080717 -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2018-02-27
  10. ^ "UCAC2 26022336 -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2018-02-27
  11. ^ 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].
  12. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  13. ^ (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.
  14. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived August 18, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  15. ^ (in Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived August 10, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.