S Sagittae, also known by the

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the 88 modern constellations, modern constellations visible from southern England. They are named after John Flamsteed, au ...

of 10 Sagittae, a

Classical Cepheid Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude u ...

variable in the constellation

Sagitta Sagitta is a dim but distinctive constellation in the northern sky. Its name is Latin for 'arrow', not to be confused with the significantly larger constellation Sagittarius 'the archer'. It was included among the 48 constellations listed by t ...

that varies from magnitude 5.24 to 6.04 in 8.382 days. It is faintly visible to the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

of an observer far from city lights. Its

variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...

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 binaries as well as qua ...

discovered its changing radial velocity in 1903–04.

Harlow Shapley Harlow Shapley (November 2, 1885 – October 20, 1972) was an American astronomer, who served as head of the Harvard College Observatory from 1921–1952, and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid var ...

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 Classical Cepheid variables G-type supergiants Sagittae, S Durchmusterung objects 188727 098085 7609 Sagittae, 10