Upsilon Sagittarii
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 21m 43.62284s |
| Declination | −15° 57′ 18.0625″ |
| Apparent magnitude (V) | 4.61 |
| Characteristics | |
| Spectral type | A2 Ia + B2 Vpe |
| U−B color index | −0.53 |
| B−V color index | +0.10 |
| Variable type | PV Tel (β Lyr?) |
| Astrometry | |
| Radial velocity (Rv) | 8.9 km/s |
| Proper motion (μ) | RA: 1.34 mas/yr Dec.: −6.25 mas/yr |
| Parallax (π) | 1.83±0.23 mas |
| Distance | approx. 1,800 ly (approx. 550 pc) |
| Absolute magnitude (MV) | −4.73 / −1.14 |
| Orbit | |
| Period (P) | 137.9 days |
| Semi-major axis (a) | 270.8 R☉ |
| Eccentricity (e) | 0 |
| Inclination (i) | 50° |
| Semi-amplitude (K1) (primary) | 49.6 km/s |
| Semi-amplitude (K2) (secondary) | 29.7 km/s |
| Details | |
| "visible" | |
| Mass | 2.5 + 4 M☉ |
| Radius | 23 R☉ |
| Luminosity | 4,700 L☉ |
| Surface gravity (log g) | 1.2 cgs |
| Temperature | 12,300 K |
| Metallicity [Fe/H] | −0.2 dex |
| Rotational velocity (v sin i) | ≤10 km/s |
| Age | 52 Myr |
| "invisible" | |
| Mass | 6.2 M☉ |
| Radius | 2.2 R☉ |
| Luminosity | 1,300 L☉ |
| Surface gravity (log g) | 1.0 cgs |
| Temperature | 23,000 K |
| Rotational velocity (v sin i) | 250 km/s |
| Other designations | |
| υ Sagittarii, υ Sgr, Upsilon Sgr, 46 Sagittarii, BD−16°5283, FK5 727, GC 26697, HD 181615, HD 181616, HIP 95176, HR 7342, PPM 235885, SAO 162518 | |
| Database references | |
| SIMBAD | data |
Upsilon Sagittarii (Upsilon Sgr, υ Sagittarii, υ Sgr) is a spectroscopic binary star system in the constellation Sagittarius. Upsilon Sagittarii is the prototypical hydrogen-deficient binary (HdB), and one of only four such systems known. The unusual spectrum of hydrogen-deficient binaries has made stellar classification of Upsilon Sagittarii difficult.