Lambda Cygni

Lambda Cygni (λ Cyg) is a class B5V (blue main-sequence) star in the constellation Cygnus. Its apparent magnitude is 4.54^[2] and it is approximately 770 light years away based on parallax.^[1]

Lambda Cygni

Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	20h 47m 24.53766s[1]
Declination	+36° 29′ 26.5737″[1]
Apparent magnitude (V)	4.54[2]
Characteristics
Spectral type	B5Ve[3]
U−B color index	−0.50 [2]
B−V color index	−0.11 [2]
Variable type	Be star[4]
Astrometry
Radial velocity (Rv)	-23.20[5] km/s
Proper motion (μ)	RA: +14.71[1] mas/yr Dec.: −8.96[1] mas/yr
Parallax (π)	4.24±0.43 mas[1]
Distance	approx. 770 ly (approx. 240 pc)
Details
λ Cyg Aa
Mass	6.40[6] M☉
Radius	3.56[7] R☉
Surface gravity (log g)	3.195[8] cgs
Temperature	13,925[8] K
Rotational velocity (v sin i)	133[8] km/s
λ Cyg Ab
Mass	6.40[6] M☉
λ Cyg B
Mass	5.12[6] M☉
Other designations
54 Cygni, CCDM J20475+3629, GC 28994, HIP 102589, HR 7963, HD 198183, SAO 70505, WDS J20474+3629
Database references
SIMBAD	data

Lambda Cygni is a multiple star, with components A, B, and C observed in the 19th century; the main component, A, is a spectroscopic binary itself with two components Aa and Ab reported at magnitudes 5.4 and 5.8 orbiting with a period of 12 years.^[9] Component B has type B7V, magnitude 6.26, and separation 0.77" (about 180 AU based on parallax).^[9][10] Component C has reported type K2III-IV, apparent magnitude 9.65, and separation about 85".^[11] Recent observations indicate the presence of additional smaller companions D (about 50" from A), E (about 8" from C), and F (about 40" from C) all around apparent magnitude 14.^[11]