W Sagittarii, also named Dhanusaragra, is a multiple star system star in the constellation Sagittarius, and a Cepheid variable star. W Sagittarii is an optical line-of-sight companion nearly a degree from the much brighter γ2 Sgr (Alnasl) which marks the nozzle or spout of the teapot asterism.
Nomenclature W Sagittarii (abbreviated W Sgr) is this star's variable star designation; it also has the Bayer designation Gamma1 Sagittarii (γ1 Sagittarii, γ1 Sgr). Dhanuśarāgra (धनुशराग्र), the Arrow, is an Indian star name used since the 14th century for the pair γ1 and γ2 Sgr, the latter having the Arabic name Alnasl. The IAU Working Group on Star Names adopted the name Dhanusaragra for γ1 Sgr Aa1 on 13 August 2026.
System 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 Aa1, Aa2, and Ab. These have also been referred to as components Aa, Ab, and B respectively. The outer companion Ab 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☉.
Variability
In early June of 1866, Johann Friedrich Julius Schmidt discovered that the star is a variable star. The supergiant component W Sgr Aa1 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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