W Sagittarii
 Location of W Sgr (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 05m 01.22409s |
| Declination | −29° 34′ 48.3199″ |
| Apparent magnitude (V) | 4.29 - 5.14 |
| Characteristics | |
| A | |
| Spectral type | F4 - G2Ib + ~F5V |
| U−B color index | +0.52 |
| B−V color index | +0.78 |
| Variable type | δ Cep |
| B | |
| Spectral type | A0 V |
| Astrometry | |
| Radial velocity (Rv) | –28.04 km/s |
| Proper motion (μ) |
RA: +2.62 mas/yr Dec.: –5.28 mas/yr |
| Parallax (π) | 2.28 ± 0.20mas |
| Distance | 409pc |
| Absolute magnitude (MV) | −3.76 |
| Orbit | |
| Primary | Aa |
| Companion | Ab |
| Period (P) | 1,582 ± 3 days |
| Semi-major axis (a) | 12.9 ± 0.3" (5.67 ± 0.13 AU) |
| Eccentricity (e) | 0.41 ± 0.02 |
| Inclination (i) | 7.0 ± 0.8° |
| Longitude of the node (Ω) | 68.4 ± 4.0° |
| Periastron epoch (T) | 2004.16 ± 0.01 |
|
Argument of periastron (ω) (secondary) |
328.0 ± 1.3° |
| Orbit | |
| Primary | A |
| Companion | B |
| Period (P) | 172.9 yr |
| Semi-major axis (a) | 63 AU |
| Details | |
| A | |
| Mass | 5.8 M☉ |
| Radius | 61.0 R☉ |
| Luminosity | 2,690 L☉ |
| Surface gravity (log g) | 1.50 - 2.15 cgs |
| Temperature | 5,380 - 6,474 K |
| Metallicity [Fe/H] | +0.02 dex |
| B | |
| Mass | 2.2 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
W Sagittarii (W Sgr, Gamma-1 Sagittarii (γ¹ Sgr)) is a multiple star system star in the constellation Sagittarius. It is an optical line-of-sight companion to the much brighter Al Nasl (γ2 Sgr) which marks the "nozzle" ("spout") of the "teapot" asterism forming a large part of Sagittarius. The primary star is a supergiant Classical Cepheid variable.
W Sgr is listed as component A of a multiple star system catalogued as ADS 11029 and WDS J18050-2935. Components B and C are at 33" and 46" respectively and both are 13th magnitude. They are purely optical companions, not physically associated with W Sgr.
Component A, W Sgr, is itself a triple star system, with the components referred to as W Sgr Aa, Ab, and B. The outer companion B has been resolved at a separation of 0.14" and is over 5 magnitudes fainter than the primary supergiant. The inner components can only be identified spectroscopically by their radial velocity variations. The primary is a 6 M☉ yellow supergiant, while the secondary is an early F main sequence star with a mass less than 1.4 M☉.
The supergiant component W Sgr Aa is a variable star which pulsates regularly between magnitudes 4.3 and 5.1 every 7.59 days. During the pulsations, that temperature and spectral type also vary. It is classified as a Classical Cepheid (δ Cephei) variable.
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