Sun (left), 61 Cygni A (bottom) and 61 Cygni B (upper right)''
61 Cygni, sometimes called Bessel's Star or Piazzi's Flying Star, is a binary star system in the constellation Cygnus. It consists of a pair of K-type dwarf stars that orbit each other in a period of about 659 years, forming a visual binary. At fifth and sixth apparent magnitudes, they are among the least conspicuous stars visible in the night sky to an observer without an optical instrument.
61 Cygni first attracted the attention of astronomers because of its large proper motion. In 1838, Friedrich Wilhelm Bessel measured its distance from Earth at about 10.4 light years, very close to the actual value of about 11.4 light years; this was the first distance estimate for any star other than the Sun, and first star to have its stellar parallax measured. Over the course of the twentieth century, several different astronomers reported detections of a massive planet orbiting one of the two stars, but recent high-precision radial velocity observations have shown that all such claims were erroneous. To date, no planets have been confirmed in this system and all of the past claims are now considered spurious.
Although it appears to be a single star to the naked eye, 61 Cygni is in fact a widely separated binary system, composed of two K class (orange) main sequence stars, 61 Cygni A and 61 Cygni B. The brighter star 61 Cygni A is of apparent magnitude 5.2, the fainter 61 Cygni B is 6.1. Both appear to be old-disk stars, with an estimated age that is older than the Sun. The system has a net space velocity of 108 km/s28 relative to the Sun, which results in the high proper motion across the sky.At a distance of just over 11 light years, it is one of the nearest star systems to the Earth. This system will make its closest approach at about 20,000 CE, when the separation from the Sun will be about 9 light years.
The two orbit their common barycenter in a period of 659 years, with a mean separation of about 84 A.U.—84 times the separation between the Earth and the Sun. The relatively large orbital eccentricity of 0.48 means that the two stars are separated by about 44 A.U. at periapsis and 124 A.U. at apoapsis. The leisurely orbit of the pair has made it difficult to pin down their respective masses, and the accuracy of these values remain somewhat controversial. In the future this issue may be resolved through the use of asteroseismology.
Component A has about 11% more mass than component B. It has an activity cycle that is much more pronounced than the solar sunspot cycle. This is a complex activity cycle that varies with a period of about 7.5±1.7 years. (An earlier estimate gave a period of 7.3 years.) The combination of starspot activity combined with rotation and chromospheric activity is characteristic of a BY Draconis variable. Because of differential rotation, this star's surface rotation period varies by latitude from 27 to 45 days, with an average period of 35 days.
The outflow of the stellar wind from component A produces a bubble within the local interstellar cloud. Along the direction of the star's motion within the Milky Way, this extends out to a distance of only 30 AU, or roughly the orbital distance of Neptune from the Sun. This is lower than the separation between the two components of 61 Cygni, and so the two most likely do not share a common atmosphere. The compactness of the astrosphere is likely due to the low mass outflow and the relatively high velocity through the local medium.
Component B displays a more chaotic pattern of variability than A, with significant short-term flares. There is an 11.7 year periodicity to the overall activity cycle of B. Both stars exhibit stellar flare activity, but the chromosphere of component B is 25% more active than for component A.33 As a result of differential rotation, the period of rotation varies by latitude from 32 to 47 days, with an average period of 38 days.
61 Cygni is frequently used in Space Opera:
- The Foundation Series, novels by Isaac Asimov. 61 Cygni has one of the planets where the human race might have originated, mentioned by the Imperial politician Lord Dorwin.
- Mission of Gravity, novel, and other stories (1953-) by Hal Clement?. 61 Cygni A is the sun around which the planet Mesklin? revolves.
- Revelation Space? stories (2000-) by Alastair Reynolds?. 61 Cygni (or 'Swan') is the sun of the planet Sky's Edge?.
- Blake's 7?, television program. The region around 61 Cygni is the only area near Earth that has not been surveyed, since it is home to an alien race which is hostile to mankind, going so far as to release a virus on a Federation base via a piece of space debris.
- Earth & Beyond?, online role-playing game. 61 Cygni is a system in the outskirts of the universe.
- Frontier?: Elite II and Frontier: First Encounters, computer games. 61 Cygni has a terraformed planet (named Scott?) that is notorious for its harsh, icy environment. Surprisingly, it has a successful tourism industry to go along with its renowned fishing industry. Its pool of tourists is derived from the populations of nearby mining systems, who would never otherwise experience a true outdoor environment where it not for the planet Scott being nearby. 61 Cygni is also a member of the Federation.
- In the Traveller universe?, 61 Cygni is the location of Nusku?, a major colony world that was strategically important during the Interstellar Wars in the 22nd century.
- While never stated on film, 61 Cygni is stated by secondary Star Trek? materials as the location of Tellar?, home of the Tellarite? species. The Star Fleet Technical Manual depicts the flag and seal of the "United Planets of 61 Cygni?," presumably the Tellarite government.
- In C.J. Cherryh's Alliance-Union future history, 61 Cygni is the site of Bryant's Star Station, one of the stations on the "Great Circle" chain of space stations that terminates at Pell Station in the Tau Ceti system.