Epoch J2000 Equinox J2000
|Right ascension||17h 10m 22.68689s|
|Declination||–15° 43′ 29.6639″|
|Apparent magnitude (V)||2.43 (3.05/3.27)|
|Spectral type||A1 IV + A1 IV|
|U−B color index||+0.09|
|B−V color index||+0.05|
|Radial velocity (Rv)||–0.9 km/s|
|Proper motion (μ)||RA: +40.13 mas/yr
Dec.: +99.17 mas/yr
|Parallax (π)||36.91 ± 0.80 mas|
|Distance||88 ± 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 dex|
|η Oph A|
|Radius||2.5/2.0 R☉|
|Luminosity||35/21 L☉|
|Temperature||8900/8600 K|
|Rotational velocity (v sin i)||23 km/s|
|η Oph B|
η Oph is actually a binary star system that is difficult to resolve in amateur telescopes but whose true nature has been determined through use of more advanced techniques. The "primary" star (whose observational data make up the table in this article), which could nominally be referred to as η Oph A, is actually only slightly larger and hotter than its companion, η Oph B. 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.
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 (pattern of stars) representing eleven old states in China that mark the left borderline of the enclosure, consisting of η Ophiuchi, δ Herculis, λ Herculis, μ Herculis, ο Herculis, 112 Herculis, ζ Aquilae, θ1 Serpentis, η Serpentis, ν Ophiuchi and ξ Serpentis. Consequently, η Ophiuchi itself is known as 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).
- 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
- Hoffleit, D.; Warren, Jr., W. H. (1991). "Entry for HR 2491". Bright Star Catalogue, 5th Revised Ed. (Preliminary Version). CDS. ID V/50.
- 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
- Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953QB901.W495.....
- . arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637. Missing or empty
- 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
- (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.
- (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.