51 Ophiuchi
51 Ophiuchi is a single star located approximately 410 light years away from the Sun in the equatorial constellation of Ophiuchus, northwest of the center of the Milky Way. It is visible to the naked eye as a faint, blue-white point of light with an apparent visual magnitude of 4.81. The star is moving closer to the Earth with a heliocentric radial velocity of –12 km/s.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ophiuchus |
| Right ascension | 17h 31m 24.95413s |
| Declination | −23° 57′ 45.5136″ |
| Apparent magnitude (V) | 4.81 |
| Characteristics | |
| Spectral type | B9.5IIIe |
| U−B color index | –0.06 |
| B−V color index | +0.00 |
| Astrometry | |
| Radial velocity (Rv) | –12 km/s |
| Proper motion (μ) | RA: 5.24 mas/yr Dec.: −25.72 mas/yr |
| Parallax (π) | 8.04 ± 0.24 mas |
| Distance | 410 ± 10 ly (124 ± 4 pc) |
| Details | |
| Mass | 3.3±0.1 M☉ |
| Radius | 5.66±0.23 R☉ |
| Luminosity | 3.12 L☉ |
| Temperature | 9,772 K |
| Metallicity [Fe/H] | –0.25 dex |
| Rotational velocity (v sin i) | 267 ± 5 km/s |
| Age | 0.3 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
This object is notable for being "a rare, nearby example of a young planetary system just entering the last phase of planet formation". There is uncertainty about the stellar classification of this star. It has the nominal classification of B9.5IIIe, a B-type giant star with emission lines. However, it has also been classified as an A0 II-IIIe star and as a Herbig Ae/Be star. 51 Ophiuchi is about 300,000 years old with 3.3 times the mass of the Sun and a polar radius 5.7 times the Sun's radius. It is radiating three times the Sun's luminosity from its photosphere at an effective temperature of 9,772 K. The star is spinning rapidly with a projected rotational velocity of 267 km/s, close to the critical rotation rate.