Epsilon Ophiuchi
Template:Location mark Location of ε Ophiuchi (circled) | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ophiuchus |
| Right ascension | Template:RA[1] |
| Declination | Template:DEC[1] |
| Apparent magnitude (V) | 3.220[2] |
| Characteristics | |
| Spectral type | G9.5 IIIb[3] |
| U−B Template:Engvar | +0.762[2] |
| B−V Template:Engvar | +0.972[2] |
| Astrometry | |
| Radial velocity (Rv) | −10.3[4] km/s |
| Proper motion (μ) | RA: +83.40[1] mas/yr Dec.: +40.58[1] mas/yr |
| Parallax (π) | 30.5136±0.1878 mas[5] |
| Distance | Template:Rnd ± Template:Rnd ly (Template:Rnd ± Template:Rnd pc) |
| Absolute magnitude (MV) | +0.55[6] |
| Details | |
| Mass | Template:Val[7] Template:Solar mass |
| Radius | Template:Val[7] Template:Solar radius |
| Luminosity | 54[8] Template:Solar luminosity |
| Surface gravity (log g) | Template:Val[3] cgs |
| Temperature | Template:Val[3] K |
| Metallicity [Fe/H] | Template:Val[3] dex |
| Rotational velocity (v sin i) | 5.7[9] km/s |
| Age | 0.95–1.01[10] Gyr |
| Metallicity [Fe/H] | {{{metal_fe2}}} dex |
| Other designations | |
| Template:Odlist[11] | |
| Database references | |
| SIMBAD | data |
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Epsilon Ophiuchi or ε Ophiuchi, formally named Yed Posterior (Template:IPAc-en),[12][13] is a red giant[7] star in the constellation of Ophiuchus. Located less than five degrees south of the celestial equator in the eastern part of the constellation,[1] it forms a naked eye optical double with Delta Ophiuchi (named Yed Prior[13]). With an apparent visual magnitude of 3.220,[2] the star can be seen with the naked eye from most of the Earth under suitably dark skies. Parallax measurements yield an estimated distance of Template:Convert 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 Arabic يد yad meaning "hand". Epsilon and Delta Ophiuchi comprise the left hand of Ophiuchus (the Serpent Bearer) that holds the head of the serpent (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, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Right Wall of Heavenly Market Enclosure, refers to an asterism which represents eleven ancient states in China and which mark the right borderline of the enclosure, consisting of Delta Ophiuchi, Beta Herculis, Gamma Herculis, Kappa Herculis, Gamma Serpentis, Beta Serpentis, Alpha Serpentis, Delta Serpentis, Epsilon Serpentis, Epsilon Ophiuchi and Zeta Ophiuchi.[17] Consequently, the Chinese name for Epsilon Ophiuchi itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx), 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 stellar classification of G9.5 IIIb, with the 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.[22] The outer envelope of this star displays solar-type oscillations with a period of 0.19 days, allowing the methods of asteroseismology to be applied.[7] However, the models for this star have not been able to distinguish whether this star is generating energy by the 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
External links
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<ref>tag; no text was provided for refs namedallen1963 - ↑ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.
- ↑ Star Names - R.H.Allen p.302
- ↑ Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ↑ Template:In lang English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ↑ Star Names - R.H.Allen p.142
- ↑ Script error: No such module "Citation/CS1".