Epsilon Ophiuchi

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Epsilon Ophiuchi
Location of ε Ophiuchi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension 16h 18m 19.28974s[1]
Declination −04° 41′ 33.0345″[1]
Apparent magnitude (V) 3.220[2]
Characteristics
Spectral type G9.5 IIIb[3]
U−B color index +0.762[2]
B−V color index +0.972[2]
Distance
106.9 ± 0.7 ly
(32.8 ± 0.2 pc)
Absolute magnitude (MV)+0.55[6]
Details
Gyr
HR 6075, SAO 141086[11]
Database references
SIMBADdata

Epsilon Ophiuchi or ε Ophiuchi, formally named Yed Posterior (

suitably dark skies. Parallax measurements yield an estimated distance of 106.4 light-years (32.6 parsecs) from the Sun
.

Nomenclature

ε Ophiuchi (Latinised to Epsilon Ophiuchi) is the star's Bayer designation.

It bore the traditional name Yed Posterior. Yed derives from the

Serpens Caput). Epsilon is Yed Posterior as it follows Delta across the sky. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN approved the name Yed Posterior for this star on 5 October 2016 and it is now so included in the List of IAU-approved Star Names.[13]

Epsilon Ophiuchi was a member of the indigenous Arabic asterism al-Nasaq al-Yamānī, the "Southern Line" of al-Nasaqān the "Two Lines",[15] along with Alpha Serpentis, Delta Serpentis, Epsilon Serpentis, Delta Ophiuchi, Zeta Ophiuchi and Gamma Ophiuchi.[16]

In

Chinese name for Epsilon Ophiuchi itself is 天市右垣十 (Tiān Shì Yòu Yuán shí, English: the Tenth Star of Right Wall of Heavenly Market Enclosure), representing the state Chu (楚) (or Tsoo),[18][19][20] together with Phi Capricorni (or 24 Capricorni in R.H.Allen's version[21]) in the Twelve States
(asterism).

Properties

Epsilon Ophiuchi has a

luminosity class of III indicating that this is a giant star that has exhausted the hydrogen and evolved away from the main sequence. This red giant has nearly double the Sun's mass and has expanded to an estimated radius of over ten times the radius of the Sun,[10] giving it a luminosity of about 54 times the Sun.[8] It is about a billion years old.[10]

Unusually for a class G giant, it is cyanogen-deficient and carbon-deficient.

thermonuclear fusion of hydrogen along a shell, or the fusion of helium at its core. Either model produces a good fit to the star's physical properties.[7] The projected rotational velocity of the star is 5.7 km s−1, and the inclination of the rotation axis to the line of sight from the Earth lies in the range of 41–73°.[9]

References

  1. ^
    S2CID 18759600
    .
  2. ^
    doi:10.1093/mnras/172.3.667
  3. ^
    S2CID 53480665
  4. Bibcode:1953GCRV..C......0W
  5. doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR
    .
  6. S2CID 16258166
  7. ^
    S2CID 15699426
  8. ^
    S2CID 121883397
  9. ^
    S2CID 30911563
  10. ^
    S2CID 250665105
  11. Centre de Données astronomiques de Strasbourg
    , retrieved 2012-01-08
  12. ISBN 978-1-931559-44-7
    .
  13. ^ a b c "Naming Stars". IAU.org. Retrieved 16 December 2017.
  14. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  15. ISBN 1-931559-44-9
  16. ISBN 0-486-21079-0, retrieved 2010-12-12 {{citation}}: ISBN / Date incompatibility (help
    )
  17. ISBN 978-986-7332-25-7
    .
  18. ^ Star Names - R.H.Allen p.302
  19. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived August 19, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  20. ^ (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.
  21. ^ Star Names - R.H.Allen p.142
  22. doi:10.1086/191542
    .
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