63 Ophiuchi
Star in the constellation Sagittarius
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63 Ophiuchi is an O-type giant star in the constellation Sagittarius, despite its name. During a 2009 survey for companions of massive stars, it was observed using speckle interferometry but no companion was found.[9] The small parallax measurement of 0.91±0.09 mas suggest that this extremely luminous star may be located about 3,600 light-years away. An estimate of the distance based on the strength of the Ca II line yields a more modest value of 2,605 ly (799 pc).[10] The star lies only 0.3° north of the galactic plane.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Sagittarius[1] |
| Right ascension | 17h 54m 54.04315s[2] |
| Declination | −24° 53′ 13.5444″[2] |
| Apparent magnitude (V) | 6.20[3] |
| Characteristics | |
| Spectral type | O8II((f))[4] |
| U−B color index | –0.89[5] |
| B−V color index | +0.04[5] |
| Astrometry | |
| Radial velocity (Rv) | –11[6] km/s |
| Proper motion (μ) | RA: +0.704[2] mas/yr Dec.: –2.194[2] mas/yr |
| Parallax (π) | 0.9071±0.0882 mas[2] |
| Distance | 3,600 ± 300 ly (1,100 ± 100 pc) |
| Absolute magnitude (MV) | −5.14±0.22[7] |
| Details | |
| Mass | 17±4[7] M☉ 29[8] M☉ |
| Radius | 12.0±1.2[7] R☉ |
| Luminosity | 11,500+820 −770[7] L☉ |
| Surface gravity (log g) | 3.51±0.03[7] cgs |
| Temperature | 35,000±300[7] K |
| Rotational velocity (v sin i) | 48±5[7] km/s |
| Age | 3.7[7] Myr |
| Other designations | |
| 63 Oph, CD−24°13615, HD 162978, HIP 87706, HR 6672, SAO 185928 | |
| Database references | |
| SIMBAD | data |
In 1983, astronomers from the Sternberg Astronomical Institute in Moscow, Russia identified a faint, shell-shaped nebula surrounding the star that was being excited by the star's energy. Named Sharpless 22, this ring-shaped nebula has a double-shell structure with an inner envelope spanning 45–50′ (9–18 pc), surrounded by a diffuse envelope some 65–80′ (14–29 pc) across. At an estimated mass loss rate of (6–8) × 10−6 M☉/yr, it would take the star about (1–5) × 105 years to produce such a nebula from the outflow of its stellar wind.[11]
In 2025 the star was found to have a weak magnetic field, which is unusual for giant stars. It is considered an example of an transitional object between main sequence strongly magnetic stars and magnetic supergiants like Alnitak.[7]