Epsilon Ophiuchi
Epsilon Ophiuchi or ε Ophiuchi, formally named Yed Posterior (/ˌjɛd pɒˈstɪəriər/), is a red giant star 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.
| 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) | 30.5136 ± 0.1878 mas |
| Distance | 106.9 ± 0.7 ly (32.8 ± 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 | |
Yed Posterior, ε Oph, Epsilon Oph, 2 Ophiuchi, BD–04 4086, FK5 605, HD 146791, HIP 79882, HR 6075, SAO 141086 | |
| Database references | |
| SIMBAD | data |
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