P Cygni
Encyclopedia
P Cygni is a variable star
in the constellation
Cygnus
. The designation
"P" was originally assigned by Johann Bayer
in Uranometria
as a nova
.
It is a hypergiant
luminous blue variable
(LBV) star of spectral type
B1Ia+ that is one of the most luminous stars in the Milky Way
galaxy. The star is located about 5000 to 6000 light years from the Earth. It was unknown until the end of the 16th century, when it suddenly brightened to 3rd magnitude
. It was first observed on 18 August (Gregorian) 1600 by Willem Janszoon Blaeu
, a Dutch astronomer, mathematician and globe-maker. After six years the star faded slowly, dropping below naked-eye visibility in 1626. It brightened again in 1655, but had faded by 1662. Another outburst took place in 1665; this was followed by numerous fluctuations. Since 1715, however, P Cygni has been a fifth magnitude star, with only minor fluctuations in brightness. Today it has a magnitude of 4.8 ± 0.5.
Due to its erratic nature, P Cygni has sometimes been called a "permanent nova"; however, its behaviour is no longer thought to involve the same processes associated with true nova
e.
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 SN 2006gy
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 redshift
ed and the absorption lobe is blueshifted with respect to the spectral line's rest wavelength. These profiles are useful in the study of stellar wind
s in many types of stars. They are often cited as an indicator of a luminous blue variable
star.
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Cygnus
Cygnus (constellation)
Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...
. The designation
Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellation's Latin name...
"P" was originally assigned by Johann Bayer
Johann Bayer
Johann Bayer was a German lawyer and uranographer . He was born in Rain, Bavaria, in 1572. He began his study of philosophy in Ingolstadt in 1592, and moved later to Augsburg to begin work as a lawyer. He grew interested in astronomy during his time in Augsburg...
in Uranometria
Uranometria
Uranometria is the short title of a star atlas produced by Johann Bayer.It was published in Augsburg, Germany, in 1603 by Christophorus Mangus under the full title Uranometria : omnium asterismorum continens schemata, nova methodo delineata, aereis laminis expressa. This translates to...
as a nova
Nova
A nova is a cataclysmic nuclear explosion in a star caused by the accretion of hydrogen on to the surface of a white dwarf star, which ignites and starts nuclear fusion in a runaway manner...
.
It is a hypergiant
Hypergiant
A hypergiant is a star with a tremendous mass and luminosity, showing signs of a very high rate of mass loss.-Characteristics:...
luminous blue variable
Luminous blue variable
Luminous blue variables, also known as S Doradus variables, are very bright, blue, hypergiant variable stars named after S Doradus, the brightest star of the Large Magellanic Cloud. They exhibit long, slow changes in brightness, punctuated by occasional outbursts in brightness during substantial...
(LBV) star of spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
B1Ia+ that is one of the most luminous stars in the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy. The star is located about 5000 to 6000 light years from the Earth. It was unknown until the end of the 16th century, when it suddenly brightened to 3rd magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
. It was first observed on 18 August (Gregorian) 1600 by Willem Janszoon Blaeu
Willem Blaeu
Willem Janszoon Blaeu , also abbreviated to Willem Jansz. Blaeu, was a Dutch cartographer, atlas maker and publisher....
, a Dutch astronomer, mathematician and globe-maker. After six years the star faded slowly, dropping below naked-eye visibility in 1626. It brightened again in 1655, but had faded by 1662. Another outburst took place in 1665; this was followed by numerous fluctuations. Since 1715, however, P Cygni has been a fifth magnitude star, with only minor fluctuations in brightness. Today it has a magnitude of 4.8 ± 0.5.
Due to its erratic nature, P Cygni has sometimes been called a "permanent nova"; however, its behaviour is no longer thought to involve the same processes associated with true nova
Nova
A nova is a cataclysmic nuclear explosion in a star caused by the accretion of hydrogen on to the surface of a white dwarf star, which ignites and starts nuclear fusion in a runaway manner...
e.
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
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
. The recent supernova SN 2006gy
SN 2006gy
SN 2006gy was an extremely energetic supernova, sometimes referred to as a hypernova or quark-nova, that was discovered on September 18, 2006. It was first observed by Robert Quimby and P. Mondol, and then studied by several teams of astronomers using facilities that included the Chandra, Lick, and...
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
Astronomical spectroscopy
Astronomical spectroscopy is the technique of spectroscopy used in astronomy. The object of study is the spectrum of electromagnetic radiation, including visible light, which radiates from stars and other celestial objects...
called a P Cygni profile, where the presence of both absorption and emission in the spectral line
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
profile indicate the existence of a gaseous envelope expanding away from the star. The emission lobe is redshift
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
ed and the absorption lobe is blueshifted with respect to the spectral line's rest wavelength. These profiles are useful in the study of stellar wind
Stellar wind
A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.Different types of stars have...
s in many types of stars. They are often cited as an indicator of a luminous blue variable
Luminous blue variable
Luminous blue variables, also known as S Doradus variables, are very bright, blue, hypergiant variable stars named after S Doradus, the brightest star of the Large Magellanic Cloud. They exhibit long, slow changes in brightness, punctuated by occasional outbursts in brightness during substantial...
star.