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|
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.
It bore the traditional name Sabik. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Sabik for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.
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. Consequently, Eta 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).
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