57 Cygni

57 Cygni is a close binary star^[4] system in the constellation Cygnus, located about 530 light years from Earth. It is visible to the naked eye as a blue-white hued star with a baseline apparent visual magnitude of 4.80.^[2] The pair have a magnitude difference of 0.34.^[4] This system is moving closer to the Earth with a heliocentric radial velocity of −21 km/s.^[2]

57 Cygni

Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	20h 53m 14.75503s[1]
Declination	+44° 23′ 14.1408″[1]
Apparent magnitude (V)	4.80[2]
Characteristics
Spectral type	B5 V[3]
B−V color index	−0.134±0.006[2]
Astrometry
Radial velocity (Rv)	−21.1±2.8[2] km/s
Proper motion (μ)	RA: +11.94[1] mas/yr Dec.: −2.08[1] mas/yr
Parallax (π)	6.21±0.22 mas[1]
Distance	530 ± 20 ly (161 ± 6 pc)
Absolute magnitude (MV)	−1.23[2]
Orbit[4]
Period (P)	2.8548 days
Eccentricity (e)	0.139±0.014[5]
Inclination (i)	≈ 48[6]°
Periastron epoch (T)	2441571.275 JD
Argument of periastron (ω) (secondary)	159.6°
Semi-amplitude (K1) (primary)	111.9 km/s
Semi-amplitude (K2) (secondary)	126.0 km/s
Details
57 Cyg A
Mass	5.54±0.55[5] M☉
Radius	3.3±0.4[4] R☉
Temperature	17,190[7] K
Rotational velocity (v sin i)	40[8] km/s
57 Cyg B
Mass	4.92±0.49[5] M☉
Radius	2.9±0.4[4] R☉
Rotational velocity (v sin i)	30[8] km/s
Other designations
57 Cyg, BD+43°3755, HD 199081, HIP 103089, HR 8001, SAO 50180[9]
Database references
SIMBAD	data

This is a double-lined spectroscopic binary with an orbital period of 2.85 days and an eccentricity of 0.15.^[4] They show a steady change in their longitude of periastron, showing an apsidal period of 203±4 years.^[10] The system does not form an eclipsing binary, having the orbital inclination of around 48°.^[6] Both components are B-type main-sequence stars with a stellar classification of B5 V.^[4]