47 Cygni

47 Cygni is a triple star system in the northern constellation of Cygnus, and is located around $1.593$ from the Earth. It is visible to the naked eye with a combined apparent visual magnitude of 4.61. The system is moving closer to the Earth with a heliocentric radial velocity of $−4.6$.

The dual nature of this system was recognized by Annie Cannon in 1912, and she assigned the pair separate Henry Draper Catalogue identifiers. They orbit each other with a period of around 52481 days. The primary component is itself a spectroscopic binary in a near circular orbit with a period of around 1117 days. The a sin i value for the primary is 30.8 ±, where a is the semimajor axis and i is the orbital inclination. It has been repeatedly resolved by speckle interferometery since 1973. Radio emission was detected from this system in 1985/86.

The supergiant primary is a slow irregular variable with an amplitude of about 0.1 magnitudes. Its angular diameter has been measured at $1,249$milliarcseconds using interferometry by the Navy Precision Optical Interferometer. At the distance of 1,249parsecs, it yield a radius of. Its close companion has 57% of the mass of the Sun. The secondary is a hot B-type main-sequence star, but still 2.5 magnitudes fainter than the primary.