Primary Aa Primary A Constellation Sagittarius B−V color index +0.78 Absolute magnitude (MV) −3.76 | Companion Ab Companion B Apparent magnitude (V) 4.29 - 5.14 Radial velocity (Rv) –28.04 km/s | |
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Similar Sagittarius, Gamma2 Sagittarii, Delta Sagittarii, Lambda Sagittarii, Epsilon Sagittarii | ||
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.
Contents
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 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☉.
Variability
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.