R Cygni 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 e ...

of the

Mira Mira (), designation Omicron Ceti (ο Ceti, abbreviated Omicron Cet, ο Cet), is a red-giant star estimated to be 200–400 light-years from the Sun in the constellation Cetus. ο Ceti is a binary stellar system, consisting of a vari ...

type in the constellation Cygnus, less than 4' from θ Cygni. This is a red giant star on the asymptotic giant branch located around 2,200 light years away. It is an

S-type star An S-type star (or just S star) is a cool giant with approximately equal quantities of carbon and oxygen in its atmosphere. The class was originally defined in 1922 by Paul Merrill for stars with unusual absorption lines and molecular bands no ...

ranging between spectral types S2.5,9e to S6,9e(Tc). Stars at this mass range and

evolutionary Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

stage are pulsationally unstable, displaying a variation in their light output. R Cygni has a maximum

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 6.1 and a minimum magnitude of 14.4, with a period of 426.45 days. The variation of this star was discovered by English astronomer

N. R. Pogson Norman Robert Pogson, CIE (23 March 1829 – 23 June 1891) was an English astronomer who worked in India at the Madras observatory. He discovered several minor planets and made observations on comets. He introduced a mathematical scale of ste ...

in 1852, and it has a history of recorded brightness measurements stretching back more than a century. R Cygni shows distinct period-doubling, where alternate maxima are of different brightness, hence the real period of pulsation could be considered to be twice that from one maximum to the next. The

Catalog of Components of Double and Multiple Stars The Catalog of Components of Double and Multiple Stars, or CCDM, is an astrometric star catalogue of double and multiple stars. It was made by Jean Dommanget and Omer Nys at the Royal Observatory of Belgium in order to provide an input cata ...

lists 10th magnitude BD+49 3065 as a companion to R Cygni, at a separation of 91", and both stars lie at approximately the same distance. The

Washington Double Star Catalog The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of June 2017) 141, ...

additionally lists a 15th magnitude star as a companion at a separation of about 14".

References

{{Stars of Cygnus S-type stars Mira variables Cygnus (constellation) Durchmusterung objects 185456 031822 Cygni, R Emission-line stars