| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 15m 12.96915s[1] |
| Declination | −20° 23′ 16.7021″[1] |
| Apparent magnitude (V) | 6.02[2] |
| Characteristics | |
| Spectral type | O9.5 III[3] |
| B−Vcolor index | 0.02[4] |
| Astrometry | |
| Radial velocity (Rv) | −11.0±1.3[5] km/s |
| Proper motion (μ) | RA: +1.60[1]mas/yr Dec.: −1.51[1]mas/yr |
| Distance | 4,600 ly (1,400[4] pc) |
| Orbit[6] | |
| Period (P) | 12.76123±0.00022 d |
| Eccentricity (e) | 0.181±0.060 |
| Periastronepoch (T) | 54005.3 ± 0.7 |
| Argument of periastron (ω) (secondary) | 156±19° |
| Semi-amplitude (K1) (primary) | 22.1±2.8 km/s |
| Details[7] | |
| 16 Sgr Aa | |
| Mass | 50[8] M☉ |
| Radius | 12.5±0.5 R☉ |
| Surface gravity (log g) | 3.3449+0.0270 −0.0247 cgs |
| Temperature | 21,691+149 −159 K |
| Metallicity [Fe/H] | 0.0123+0.0189 −0.0100 dex |
| Rotational velocity (v sin i) | 51[8] km/s |
| 16 Sgr Ab | |
| Mass | 3.72[8] M☉ |
| Other designations | |
| 16 Sgr,BD−20° 5055,HD 167263,HIP 89440,HR 6823,SAO 186544,WDS J18152-2023A[9] | |
| Database references | |
| SIMBAD | data |
16 Sagittarii is a multiple[6]star system in the southernzodiacconstellation ofSagittarius. It is near the lower limit of brightness for stars that can be seen with the naked eye, having anapparent visual magnitude of 6.02.[2] The estimated distance to this system is about 4,600 light years.[4] It is a member of the Sgr OB7 cluster.[4] Along with the O-type star15 Sgr, it is ionizing anH II region along the western edge of themolecular cloud L291.[10]
Mason et al. (1998) found this to be a member of a speckle binary with an estimatedorbital period of roughly 130 years and a magnitude difference of 0.4. Both components show indications of a variable radial velocity, suggesting that they arespectroscopic binaries – making it a candidate quadruple star system.[6] However, Tokovinin (2008) considers it a triple star system.[8]
Orbital elements for the main spectroscopic binary, components Aa and Ab,[4] were published by Mayer et al. (2014), giving an orbital period of 12.76 days and aneccentricity of 0.18.[6] This system displays a mergedstellar classification of O9.5 III,[3] matching a blue-huedO-typegiant star. It shows a longitudinalmagnetic field strength of−74±44 G and aprojected rotational velocity of 51 km/s.[11] Tokovinin (2008) gives an estimated mass of 50 times themass of the Sun for the primary, and 3.72 for the secondary. The tertiary member, component B, has 2.54 times the Sun's mass.[8]
