Epsilon Ophiuchi
 Location of ε Ophiuchi (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Ophiuchus |
| Right ascension | 16h 18m 19.28974s |
| Declination | –04° 41′ 33.0345″ |
| Apparent magnitude (V) | 3.220 |
| Characteristics | |
| Spectral type | G9.5 IIIb |
| U−B color index | +0.762 |
| B−V color index | +0.972 |
| Astrometry | |
| Radial velocity (Rv) | –10.3 km/s |
| Proper motion (μ) |
RA: +83.40 mas/yr Dec.: +40.58 mas/yr |
| Parallax (π) | 30.64 ± 0.20mas |
| Distance | 106.4 ± 0.7 ly (32.6 ± 0.2 pc) |
| Absolute magnitude (MV) | +0.55 |
| Details | |
| Mass | 1.85 ± 0.05 M☉ |
| Radius | 10.39 ± 0.07 R☉ |
| Luminosity | 54 L☉ |
| Surface gravity (log g) | 2.59 ± 0.08 cgs |
| Temperature | 4,918 ± 28 K |
| Metallicity [Fe/H] | –0.13 ± 0.06 dex |
| Rotational velocity (v sin i) | 5.7 km/s |
| Age | 0.95–1.01 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Epsilon Ophiuchi (ε Ophiuchi, abbreviated Epsilon Oph, ε Oph), also named Yed Posterior, is a red giantstar in the constellation of Ophiuchus. Located less than five degrees south of the celestial equator in the eastern part of the constellation, it forms a naked eye optical double with Delta Ophiuchi (named Yed Prior). With an apparent visual magnitude of 3.220, 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 106.4 light-years (32.6 parsecs) from the Sun.
ε Ophiuchi (Latinised to Epsilon Ophiuchi) is the star's Bayer designation.
It bore the traditional name Yed Posterior. Yed derives from the Arabic Yad meaning "the 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) 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 entered in the IAU Catalog of Star Names.
Epsilon Ophiuchi was a member of the indigenous Arabic asterism al-Nasaq al-Yamānī, the "Southern Line" of al-Nasaqān the "Two Lines", along with Alpha Serpentis, Delta Serpentis, Epsilon Serpentis, Delta Ophiuchi, Zeta Ophiuchi and Gamma Ophiuchi.
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