4 Cygni

4 Cygni is a binary star^[7] system in the northern constellation of Cygnus. It is a faintly visible to the naked eye with an apparent visual magnitude of 5.17.^[2] The distance to 4 Cygni, as determined from its annual parallax shift of 5.8 mas,^[1] is about 560 light years.

4 Cygni

Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	19h 26m 09.12787s[1]
Declination	+36° 19′ 04.4369″[1]
Apparent magnitude (V)	5.17[2]
Characteristics
Evolutionary stage	main sequence[3]
Spectral type	B8p Si (Fe II)[4]
B−V color index	−0.120±0.001[2]
Variable type	α2 CVn[5]
Astrometry
Radial velocity (Rv)	−22[6] km/s
Proper motion (μ)	RA: +3.769[1] mas/yr Dec.: +13.236[1] mas/yr
Parallax (π)	5.8357±0.1372 mas[1]
Distance	560 ± 10 ly (171 ± 4 pc)
Absolute magnitude (MV)	−1.51[2]
Orbit[7]
Period (P)	35.0225±0.0002 d
Eccentricity (e)	0.45±0.13
Periastron epoch (T)	2438929.1±1.1 JD
Argument of periastron (ω) (secondary)	290±21°
Semi-amplitude (K1) (primary)	5.7±0.6 km/s km/s
Details[3]
Mass	4.08±0.18 M☉
Radius	5.03[8] R☉
Luminosity	501+130 −103 L☉
Temperature	12,190+399 −387 K
Rotational velocity (v sin i)	30±4[9] km/s
Age	145 Myr
Other designations
4 Cyg, V1741 Cygni, BD+36°3557, FK5 3554, GC 26846, HD 183056, HIP 95556, HR 7395, SAO 68301[10]
Database references
SIMBAD	data

This is single-lined spectroscopic binary with an orbital period of 35 days and an eccentricity of 0.45.^[7] The visible component is a B-type star with a stellar classification of B8p Si (Fe II),^[4] where the suffix notation indicates this is type of chemically peculiar star known as a silicon star. It displays an overabundance of iron in the visual spectrum, while the star appears helium-weak in the ultraviolet.^[4]

4 Cygni A is an Alpha² Canum Venaticorum variable that varies by 0.02 magnitude over a period of 0.68674 days.^[5] The average quadratic field strength of the magnetic field is (254.7±57.2)×10⁻⁴ T.^[11] With an age of 145 million years, it has four^[3] times the mass of the Sun and five^[8] times the Sun's radius. It radiates around 501 times the Sun's luminosity from its photosphere at an effective temperature of 12,190 K.^[3]