Psi Sagittarii
Triple star system in the constellation Sagittarius
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Psi Sagittarii, which is Latinized from ψ Sagittarii, is a triple star[8] system in the zodiac constellation of Sagittarius. The star system is located at a distance of 298 light years from the Earth based on parallax, but is drifting closer with a heliocentric radial velocity of −12 km/s.[4] The system is faintly visible to the naked eye has a combined apparent visual magnitude of +4.86.[2]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 15m 32.42658s[1] |
| Declination | −25° 15′ 24.0569″[1] |
| Apparent magnitude (V) | +4.86[2] |
| Characteristics | |
| Spectral type | K2 III + A9 III + A3 V[3] |
| B−V color index | 0.569±0.006[2] |
| Astrometry | |
| Radial velocity (Rv) | −11.43±1.47[4] km/s |
| Proper motion (μ) | RA: +45.50[1] mas/yr Dec.: −31.08[1] mas/yr |
| Parallax (π) | 10.93±0.31 mas[1] |
| Distance | 298 ± 8 ly (91 ± 3 pc) |
| Absolute magnitude (MV) | 0.06[2] |
| Orbit[5] | |
| Period (P) | 7,319 d |
| Eccentricity (e) | 0.51 |
| Periastron epoch (T) | 2442418.795 JD |
| Argument of periastron (ω) (secondary) | 2.6° |
| Semi-amplitude (K1) (primary) | 10.0 km/s |
| Semi-amplitude (K2) (secondary) | 13.8 km/s |
| Details | |
| A | |
| Mass | 2.10[6] M☉ |
| Luminosity | 84[2] L☉ |
| Ba/Bb | |
| Mass | 1.70/2.70 M☉ |
| Other designations | |
| ψ Sgr, 42 Sgr, CPD−25°6737, HD 179950, HIP 94643, HR 7292, SAO 187882, WDS J19155-2515[7] | |
| Database references | |
| SIMBAD | data |
The inner pair of this triple star system, components Ba and Bb, have an orbital period of 10.78 days and an eccentricity of 0.47.[8] The pair consist of an A-type giant and a less evolved A-type main-sequence star with stellar classifications of A9 III + A3 V,[3] respectively. These in turn share an orbit with the primary, component A, having a period of 20 years and an eccentricity of 0.51.[5] The last is an orange-hued K-type giant with a class of K2 III.[3]
Name and etymology
This star, together with τ Sgr, ν Sgr, ω Sgr, 60 Sgr and ζ Sgr formed the Arabic asterisms Al Udḥiyy, the Ostrich's Nest, and Al Kiladah, the Necklace.[9] The catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars listed this star with the name Al Kiladah.[10]