RW Cygni is a

semiregular variable star In astronomy, a semiregular variable star, a type of variable star, is a giant or supergiant of intermediate and late (cooler) spectral type showing considerable periodicity in its light changes, accompanied or sometimes interrupted by various irre ...

in the constellation Cygnus, about a degree east of 2nd magnitude

γ Cygni Gamma Cygni (γ Cygni, abbreviated Gamma Cyg, γ Cyg), officially named Sadr , is a star in the northern constellation of Cygnus, forming the intersection of an asterism of five stars called the Northern Cross. Based upon parallax me ...

. Its

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

varies between 8.05 and 9.70 and its spectral type between M3 and M4.

Distance

The

Gaia Data Release 2 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, especia ...

parallax for RW Cyg is or a distance of around . RW Cygni is assumed to be a member of the Cygnus OB9 Stellar Association and therefore around 3,600

light-years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 101 ...

from the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

. Newer observations based on the parallaxes of neighbouring

OB star OB stars are hot, massive stars of spectral types O or early-type B that form in loosely organized groups called OB associations. They are short lived, and thus do not move very far from where they formed within their life. During their lifet ...

s give RW Cygni a distance of .

Properties

RW Cygni is a luminous

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Antar ...

with a

bolometric luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a s ...

more than . Its spectral type is given in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and th ...

as M2-4Ia-Iab, covering the range of previously published values. It has been defined as a standard star for the MK spectral classification of M3-M4Ia-Iab. In 2005, the

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

is directly calculated to be 3,600 K, giving a radius of . An alternate calculation gives a higher temperature of 3,920 K and a correspondingly lower radius of . More recent measurements based on its

parallax gives the similar effective temperature derived in 2005 and as well as a larger radius of , which would make RW Cygni one of the largest known stars. Using the more conservative figure, if it was placed at the center of

, it would be extend past the orbit of

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmos ...

and into the

Asteroid Belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

The initial mass of RW Cygni has been estimated from its position relative to theoretical

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is con ...

ary tracks to be around . Observations of its atmosphere suggest that it is losing mass at a rate of per year. RW Cygni is classified as a

. It is given the subtype SRc, indicating that it is a cool supergiant. Its brightness varies from extremes of magnitude +8.0 and +9.5 with a period of . No long secondary period has been detected.

References

{{Stars of Cygnus M-type supergiants 101023 Semiregular variable stars Cygnus (constellation) BD+39 4208 Cygni, RW IRAS catalogue objects J20285059+3958543

Distance

Properties

See also

References