Xi Scorpii
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Scorpius |
| ξ Sco ABC | |
| Right ascension | 16h 04m 22.191s |
| Declination | −11° 22′ 22.60″ |
| Apparent magnitude (V) | 4.17 (5.16 / 4.87 / 7.30) |
| ξ Sco D | |
| Right ascension | 16h 04m 25.9261s |
| Declination | −11° 26′ 57.778″ |
| Apparent magnitude (V) | 7.43 |
| ξ Sco E | |
| Right ascension | 16h 04m 26.7184s |
| Declination | −11° 26′ 59.543″ |
| Apparent magnitude (V) | 7.81 |
| Characteristics | |
| ξ Sco ABC | |
| Spectral type | F4(V) + F6(V) + G1V |
| U−B color index | +0.00 |
| B−V color index | +0.45 |
| ξ Sco DE | |
| Spectral type | K1(V) + K1(V) |
| U−B color index | +0.315 |
| B−V color index | +0.75 |
| Astrometry | |
| ξ Sco ABC | |
| Radial velocity (Rv) | -36.33 ± 0.83 km/s |
| Proper motion (μ) |
RA: -63.2 mas/yr Dec.: -27.0 mas/yr |
| ξ Sco D | |
| Radial velocity (Rv) | -31.60 ± 0.2 km/s |
| Proper motion (μ) |
RA: -63.43 mas/yr Dec.: -20.55 mas/yr |
| Parallax (π) | 35.90 ± 0.23mas |
| Distance | 90.9 ± 0.6 ly (27.9 ± 0.2 pc) |
| Orbit | |
| Primary | ξ Sco A |
| Companion | ξ Sco B |
| Period (P) | 45.90 ± 0.60 yr |
| Semi-major axis (a) | 0.654 ± 0.006″ |
| Eccentricity (e) | 0.744 ± 0.001 |
| Inclination (i) | 34.5 ± 1.0° |
| Longitude of the node (Ω) | 25.3 ± 4.0° |
| Periastron epoch (T) | B 1997.22 ± 0.02 |
|
Argument of periastron (ω) (secondary) |
163.8 ± 5.0° |
| Orbit | |
| Primary | ξ Sco AB |
| Companion | ξ Sco C |
| Period (P) | 1514.43 yr |
| Semi-major axis (a) | 7.755″ |
| Eccentricity (e) | 0.041 |
| Inclination (i) | 131.5° |
| Longitude of the node (Ω) | 47.4° |
| Periastron epoch (T) | B 2226.10 |
|
Argument of periastron (ω) (secondary) |
59.3° |
| Other designations | |
| ξ Sco A: HD 144070, HR 5978, ADS 9909 A | |
| ξ Sco B: HD 144069, HR 5977, ADS 9909 B | |
| ξ Sco C: SAO 159666, ADS 9909 C | |
| ξ Sco D: BD−11° 4057, GJ 9541 A, HD 144087, HIP 78738, SAO 159668, ADS 9910 A | |
| Database references | |
| SIMBAD | ξ Sco ABC |
| ξ Sco AB | |
| ξ Sco A | |
| ξ Sco B | |
| ξ Sco C | |
| ξ Sco D | |
| ξ Sco E | |
| ARICNS | ξ Sco A |
| ξ Sco B | |
| ξ Sco C | |
Coordinates: 
16h 04m 22.1s, −11° 22′ 23″
Xi Scorpii (ξ Sco) is a quintuple star system in the constellation of Scorpius. It was formerly known by its latter designation of 51 Librae.
ξ Scorpii (Latinized to Xi Scorpii) is the star's Bayer designation. Xi Scorpii has no Flamsteed designation, or a proper name. However, it was formerly and erroneously known as Graffias before that name was applied to Beta Scorpii. Additionally, it was formerly known as 51 Librae. When the constellations were drawn, Xi Scorpii was now located in the constellation Scorpius, and the name fell into disuse.
The five stars of Xi Scorpii all have different designations. Depending on the catalogue, however, some designations apply to more than one stars. Xi Scorpii A, B, and C appear very close together in the sky and are often given one designation, while D and E are sometimes also given a single designation.
The Xi Scorpii system consists five stars in two groups separated by about 4.7 arcminutes (or 0.08°) on the sky.
The brighter group contains Xi Scorpii A, B, and C. A and B are both yellow-white F-type stars. A is slightly brighter and warmer. They are separated by 0.744 arcseconds on average, and orbit around a common center once every 45.9 years. The dimmer, seventh-magnitude Xi Scorpii C orbits this pair at about ten times the distance, having a separation of around 7.6 arcseconds.
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