Eta Ophiuchi

Eta Ophiuchi A/B
Diagram showing star positions and boundaries of the Perseus constellation and its surroundings


Location of η Ophiuchus (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 (3.05/3.27)[2]
Characteristics
Spectral type A1 V + A3 V[3]
U−B color index 0.09
B−V color index 0.05
Astrometry
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[1] mas
Distance88 ± 2 ly
(27.1 ± 0.6 pc)
Orbit[2]
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)
(secondary)		274.8 ± 2.0°
Details
η Oph A
Mass2.966[2] M☉
Radius2.5/2.0 R☉
Luminosity35/21 L☉
Temperature8900/8600 K
Rotational velocity (v sin i)23[5] km/s
η Oph B
Mass3.478[2] 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
SIMBADdata

Eta Ophiuchi, also known as η Oph or η Ophiuchi, is a star in the constellation Ophiuchus. It has the traditional name Sabik.

Properties

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 warmer 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 impossible in this system and some stellar data imprecise.

η Oph is the northern pole star of the planet Uranus.

In culture

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.[6] 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).[7][8]

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

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 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
  2. ↑ 2.0 2.1 2.2 2.3 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
  3. ↑ Edwards, T. W. (April 1976), "MK classification for visual binary components", Astronomical Journal 81: 245–249, Bibcode:1976AJ.....81..245E, doi:10.1086/111879
  4. ↑ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953QB901.W495.....
  5. ↑ 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
  6. ↑ (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.
  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.
  8. ↑ (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.