P Cygni

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**P Cygni**
Observation data Epoch J2000
P Cygni
Constellation (pronunciation)	Cygnus
Right ascension	20h 17m 47.2018s
Declination	+38° 01' 58.549"'
Apparent magnitude (V)	4.795
Characteristics
Spectral type	B2
U-B color index	-0.58
B-V color index	+0.42
Variable type	None
Astrometry
Radial velocity (R_v)	-8.9 km/s
Proper motion (μ)	RA: -3.53 mas/yr Dec.: -6.88 mas/yr
Parallax (π)	0.52 ± 0.50 mas
Distance	approx. 6000 ly (approx. 2000 pc)
Absolute magnitude (M_V)	5.134
Details
Mass	30 M_☉
Radius	76 R_☉
Luminosity	630,000 L_☉
Temperature	19,300 K
Metallicity	?
Rotation	75 km/s (50 days)
Age	? years
Other designations
NOVA Cyg 1600, * 34 Cyg, Glazar Cyg 11, JP11 3218, TD1 26474, GSC 03151-03442, LS II +37 50, TYC 3151-3442-1, AG+37° 1953, HBHA 3703-88, 2MASS J20174719+3801585, ALS 11097, HD 193237, MCW 849, BD+37° 3871, Hen 3-1871, PLX 4837, CEL 5017, HIC 100044, PPM 84645, V* P Cyg, Hilt 916, RAFGL 5493S, GC 28218, HIP 100044, ROT 2959, GCRV 12673, HR7763, SAO 69773, AAVSO 2014+37A.
Database references
SIMBAD	data

P Cygni is a variable star in the constellation Cygnus. It is a hypergiant luminous blue variable (LBV) star of spectral type B2 Ia that is one of the most luminous stars in the Milky Way galaxy and is located about 5000 to 6000 light years from Earth. It was unknown until the 17th century, when it suddenly brightened to 3rd magnitude. It briefly disappeared and returned, and today has a magnitude of 4.8 ± 0.5.

Luminous Blue Variable stars like P Cygni are very rare and short lived, and only form in regions of galaxies where intense star formation is happening. LBV stars are so massive and energetic (typically 50 times the mass of our sun and tens of thousands of times more luminous) that they exhaust their nuclear fuel very quickly. After shining for only a few million years (compared to several billion years for our sun) they erupt in a supernova. The recent supernova SNG2006gy ^[1] was likely the end of an LBV star similar to P Cygni but located in a distant galaxy.

P Cygni gives its name to a type of spectroscopic feature called a P Cygni profile, where the presence of both absorption and emission in the spectral line profile indicate the existence of a gaseous envelope expanding away from the star. The emission lobe is redshifted and the absorption lobe is blueshifted with respect to the spectral line's rest wavelength. These profiles are useful in the study of stellar winds in many types of stars. They are often cited as an indicator of a Luminous blue variable star.