S Sagittae, also known by the Flamsteed designation of 10 Sagittae, 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 ...

variable in the constellation Sagitta that varies from magnitude 5.24 to 6.04 in 8.382 days. Its

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...

of "S" indicates that it was the second star discovered to be variable in the constellation. Irish amateur astronomer

John Ellard Gore John Ellard Gore (1845–1910) was an Irish amateur astronomer and prolific author, and a founding member of the British Astronomical Association. He was mainly interested in variable stars of which he discovered several, most notably W Cygni ...

was the first to observe its variability in 1885, and

Ralph Hamilton Curtiss Ralph Hamilton Curtiss (8 February 1880 – 25 December 1929) was an American astronomer and a professor of astrophysics at the University of Michigan. His main work was on stellar spectra and the identification of spectral Binary star, binaries a ...

discovered its changing radial velocity in 1903–04.

Harlow Shapley Harlow Shapley (November 2, 1885 – October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921–1952), and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid variable stars to estim ...

observed in 1916 that the spectrum of it and other Cepheids varied with its brightness, recording it as spectral type F0 leading to maximum, F4 at maximum, and G3 just before minimum brightness. S Sagittae is a yellow-white supergiant that varies between spectral types F6Ib and G5Ib. It is around six or seven times as massive and five thousand times as luminous as the Sun and is located around 2,000 light-years away from Earth. Its radius is 58.5 times that of the Sun. The radius, temperature, luminosity, and colour are all variable as the star pulsates during its eight-day period. The period is slowly increasing. S Sagittae has been reported as a double or triple system with a hotter main sequence star companion in a 676-day orbit. The companion, and its own possible fainter companion, are only detectable from radial velocity changes in the spectral lines of the Cepheid primary and an ultraviolet excess. Analysis of the spectrum indicates a star of spectral type A7V to F0V, and 1.5 to 1.7 times as massive as the Sun. However, as the mass of the companion is greater than 2.8 solar masses, this strongly suggests this companion is itself a binary star.

References

{{stars of Sagitta Sagitta (constellation) Classical Cepheid variables G-type supergiants Sagittae, S Durchmusterung objects 188727 098085 7609 Sagittae, 10