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31 Cygni, also known as ο1 Cygni, Omicron1 Cygni, ο2 Cygni or V695 Cygni, is a ternary star system about 750 
31 Cygni A is an Algol-type eclipsing binary and ranges between magnitudes 3.73 and 3.89 over a period of ten years. The eclipsing system has been studied in attempts to determine an accurate direct mass for a red supergiant. The value is believed to be accurate to about 2%, but there are some discrepancies in the orbital fit.
31 Cygni, also known as ο1 Cygni, Omicron1 Cygni, ο2 Cygni or V695 Cygni, is a ternary star system about 750 light year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...
s away 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 first constellati ...
Cygnus.
The Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
ο (omicron
Omicron (, ; uppercase Ο, lowercase ο, ) is the fifteenth letter of the Greek alphabet. This letter is derived from the Phoenician letter ayin: . In classical Greek, omicron represented the close-mid back rounded vowel in contrast to '' o ...
) has been variously applied to two or three of the stars 30, 31, and 32 Cygni. 31 Cygni has been designated, variously, as ο1 or ο2 Cygni — therefore for clarity, it is preferred to use 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 ...
31 Cygni.
31 Cygni consists of a visible pair of stars apart as of 2016, and the brighter of the two is also a spectroscopic binary
A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
. 31 Cygni A is also designated HD 192577 and HR 7735, while its 7th-magnitude visual companion is designated HD 192579. Some multiple star
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...
catalogues designate a 13th-magnitude star from 31 Cygni A as 31 Cygni B, and HD 192579 as 31 Cygni C. The 13th-magnitude star is likely to be an unrelated background object.
The spectroscopic pair are an orange supergiant of spectral type K3Ib and a blue-white star likely to be evolving off the main sequence with a spectral type of B2IV-V. The visible companion is a 7th-magnitude B5 main sequence star.
31 Cygni A is an Algol-type eclipsing binary and ranges between magnitudes 3.73 and 3.89 over a period of ten years. The eclipsing system has been studied in attempts to determine an accurate direct mass for a red supergiant. The value is believed to be accurate to about 2%, but there are some discrepancies in the orbital fit.
30 Cygni
30 Cygni (ο1 Cygni) is a class A5III (white giant) star in the constellation Cygnus. Its apparent magnitude is 4.83 and it is approximately 610 light years away based on parallax.
The Bayer letter ο (omicron) has been variously appli ...
is another naked eye star a tenth of a degree away, forming a bright triple.
32 Cygni is about a degree away to the north, also a detached eclipsing binary
A binary star or binary star system is a Star system, system of two stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved ...
system. It comprises a large cool evolved star
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 consi ...
and a small hot main sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
or subgiant
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...
companion.
Notes
References
{{Stars of Cygnus Cygnus (constellation) Cygni, 31 Algol variables Cygni, V695 7735 Cygni, Omicron1 192577 099675 BD+46 2882 K-type supergiants B-type main-sequence stars B-type subgiants