W Sagittarii (W Sgr, Gamma-1 Sagittarii (γ¹ Sgr)) is a

multiple star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speaki ...

star in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Sagittarius, and a

Cepheid variable star A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. A strong direct relationship between a Cepheid vari ...

. W Sagittarii is an optical line-of-sight companion nearly a degree from the much brighter γ² Sgr (Al Nasl) which marks the nozzle or spout of the

teapot A teapot is a vessel used for steeping tea leaves or a herbal mix in boiling or near-boiling water, and for serving the resulting infusion which is called tea. It is one of the core components of teaware. Dry tea is available either in tea ba ...

asterism.

System

W Sgr is listed as component A of a multiple star system catalogued as

ADS" \n\nads.txt (Authorized Digital Sellers) is an initiative from IAB Technology Laboratory. It specifies a text file that companies can host on their web servers, listing the other companies authorized to sell their products or services. This is des ...

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 Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram with absolute visual magnitudes between about −3 and −8. The temperature range of supergiant stars spa ...

. The inner components can only be identified spectroscopically by their radial velocity variations. The primary is a yellow supergiant, while the secondary is an early F main sequence star with a mass less than .

Variability

The supergiant component W Sgr Aa1 is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

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 Classical Cepheids (also known as Population I Cepheids, Type I Cepheids, or Delta Cepheid variables) are a type of Cepheid variable star. They are population I variable stars that exhibit regular radial pulsations with periods of a few days to a ...

(δ Cephei) variable.

References

{{DEFAULTSORT:W Sagittarii Sagittarius (constellation) Sagittarii, Gamma1 Sagittarii, W Classical Cepheid variables F-type supergiants G-type supergiants 5 4 Spectroscopic binaries 6742 164975 088567 F-type main-sequence stars A-type main-sequence stars Durchmusterung objects