Lambda Cephei

Lambda Cephei (λ Cephei) is a fifth magnitude blue supergiant star in the constellation Cepheus, one of the hottest and most luminous visible to the naked eye.

λ Cephei

Location of λ Cep (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Cepheus
Right ascension	22h 11m 30.57571s[1]
Declination	+59° 24′ 52.15″[1]
Apparent magnitude (V)	+5.050[2]
Characteristics
Evolutionary stage	Blue supergiant
Spectral type	O6.5If(n)p[3]
U−B color index	−0.622[2]
B−V color index	+0.237[2]
Astrometry
Radial velocity (Rv)	-75.10[4] km/s
Proper motion (μ)	RA: -7.46[1] mas/yr Dec.: -11.09[1] mas/yr
Parallax (π)	1.65±0.22 mas[1]
Distance	950[2] pc
Absolute magnitude (MV)	-6.43[2]
Details[2]
Mass	51.4 M☉
Radius	18[5] - 21[6] R☉
Luminosity	630,000 L☉
Surface gravity (log g)	3.54 cgs
Temperature	36,000 K
Rotation	210
Age	4.0 Myr
Other designations
Lambda Cephei, 22 Cephei, HD 210839, HR 8469, BD+58 2402, HIP 109556, SAO 34149, GSC 03981-01585, GC 31066
Database references
SIMBAD	data

Characteristics

It is a hot O6.5 supergiant star at a distance of approximately 1,980 light years, with an absolute brightness around half a million times that of the Sun and a radius around 20 times as big, and with a mass that has been estimated to be between 45 and 60 solar masses.

Lambda Cephei turns around its axis in less than three days compared to the 24.47 days that the Sun needs to complete a full rotation and seems to be single, with no companions. Its ultimate fate is to explode as a supernova. Due to its very large initial mass, it will most likely leave behind a black hole.

Lambda Cephei is also a runaway star that seems to have been expelled of the stellar association Cepheus OB3, that lies at 2,800 light-years, roughly 2,5 million years ago. Its motion through the interstellar medium is producing a shockwave in front of the gases that surround it and in the direction towards it moves.^[7]