59 Cygni is a multiple star system in the northern
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 origins of the e ...
light year
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 1012 ...
s away from Earth. It is visible to the naked eye as a blue-white hued star with a combined
apparent visual 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 lig ...
of 4.74.
The primary component and brightest member of this system, designated 59 Cyg Aa, is a rapidly rotating
Be star
Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...
with a
stellar classification
In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...
of B1.5 Vnne. This is a well-studied star thanks to pronounced spectral variations that have been observed since 1916, and two short-term
shell star
A shell star is a star having a spectrum that shows extremely broad absorption lines, plus some very narrow absorption lines. They typically also show some emission lines, usually from the Balmer series but occasionally of other lines. The broad ...
phases that were observed in 1973 and 1974–5. It is actually a confirmed
spectroscopic binary
A binary star is a system of two star, 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 using a telescope as separa ...
system with a high temperature
subdwarf
A subdwarf, sometimes denoted by "sd", is a star with luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral ...
orbital period
The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...
. The latter is heating the nearest side of the circumstellar gaseous disk that surrounds the primary.
Orbiting the primary pair is 59 Cyg Ab, a magnitude 7.64
A-type main-sequence star
An A-type main-sequence star (A V) or A dwarf star is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...
of class A3V, located at an
angular separation
Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer.
Angular distance appears in mathematics (in pa ...
of . A fourth component is a magnitude 9.8 A-type
giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence, main-sequence (or ''dwarf'') star of the same effective temperature, surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moo ...
of class A8III at a separation of along a
position angle
In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the north celestial pole (NCP), turning positive into the d ...
(PA) of 352°, as of 2008. The fifth companion is magnitude 11.7 at a separation of and a PA of 141°.
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 ...
suggests that the companions at and are respectively and away and moving in approximately the same direction as the primary triple.