P Cygni (34 Cyg) is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in Uranometria as a nova. Located about 5,000 to 6,000 light-years (1,500–1,800 parsecs) from Earth, 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.
Epoch J2000 Equinox J2000
|Right ascension||20h 17m 47.2018s|
|Declination||+38° 01′ 58.549″|
|Apparent magnitude (V)||4.82 (3 to 6)|
|U−B color index||-0.58|
|B−V color index||+0.42|
|Radial velocity (Rv)||-8.9 km/s|
|Proper motion (μ)|| RA: -3.53 mas/yr |
Dec.: -6.88 mas/yr
|Parallax (π)||0.32 ± 0.16 mas|
|Absolute magnitude (MV)||−7.9|
|Surface gravity (log g)||1.2 cgs|
|Rotational velocity (v sin i)||35 km/s|
Nova Cyg 1600, 34 Cyg, JP11 3218, TD1 26474, GSC 03151-03442, TYC 3151-3442-1, AG+37° 1953, 2MASS J20174719+3801585, ALS 11097, HD 193237, MCW 849, BD+37° 3871, Hen 3-1871, PLX 4837, CEL 5017, PPM 84645, P Cyg, RAFGL 5493S, GC 28218, HIP 100044, ROT 2959, GCRV 12673, HR 7763, SAO 69773, AAVSO 2014+37A.
The star is located about 5,000 to 6,000 light-years (1,500–1,800 parsecs) from Earth. Despite this vast distance, it is visible to the naked eye in suitable dark sky locations. 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. Bayer's atlas of 1603 assigned it the miscellaneous label P and the name has stuck ever since. 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 P Cygni has been a fifth magnitude star, with only minor fluctuations in brightness. Today it has a magnitude of 4.8, irregularly variable by a few hundredths of a magnitude on a scale of days. The visual brightness is increasing by about 0.15 magnitude per century, attributed to a slow decrease in temperature at constant luminosity.
P Cygni has been called a "permanent nova" because of spectral similarities and the obvious outflow of material, and was once treated with novae as an eruptive variable; however, its behaviour is no longer thought to involve the same processes associated with true novae.
P Cygni is widely considered to be the earliest known example of a luminous blue variable. However, it is far from a typical example. Typically, LBVs change in brightness with a period of years to decades, occasionally hosting outbursts where the brightness of the star increases dramatically. P Cygni has been largely unvarying both in brightness and spectrum since a series of large outbursts in the 17th century. Similar events have been seen in Eta Carinae and possibly a handful of extra-galactic objects.
P Cygni does show evidence for previous large eruptions around 900, 2,100, and possibly 20,000 years ago. In more recent centuries, it has been very slowly increasing in visual magnitude and decreasing in temperature, which has been interpreted as the expected evolutionary trend of a massive star towards a red supergiant stage.
Luminous blue variables 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 the 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 the 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 is thought to be in the hydrogen shell burning phase immediately after leaving the main sequence.
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 profile of the same spectral line indicates the existence of a gaseous envelope expanding away from the star. The emission line arises from a dense stellar wind near to the star, while the blueshifted absorption lobe is created where the radiation passes through circumstellar material rapidly expanding in the direction of the observer. 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, although they also occur in other types of star.
It has been proposed P Cygni's eruptions could be caused by mass transfer to a hypothetical companion star of spectral type B that would have a mass between 3 and 6 times the mass of the Sun and would orbit P Cygni each 7 years in a high eccentricity orbit. Infall of matter into the secondary star would produce the release of gravitational energy, part of which would cause an increase of the luminosity of the system.
AG Pegasi is a symbiotic binary star in the constellation Pegasus. It is a close binary composed of a red giant and white dwarf, estimated to be around 2.5 and 0.6 times the mass of the Sun respectively. It is classified as a symbiotic nova; it has undergone one extremely slow nova outburst and a smaller outburst.
Initially a magnitude 9 star, AG Pegasi brightened and peaked at an apparent magnitude of 6.0 around 1885 before gradually fading to magnitude 9 in the late 20th century. Its spectrum was noted by earlier observers to resemble P Cygni. The spectrum of the hotter star has changed drastically over 160 years, leading investigators Scott Kenyon and colleagues to surmise that its hotter component, originally a white dwarf, accumulated enough material from the donor giant star to begin burning hydrogen and enlarge and brighten into an A-type white supergiant around 1850. It had this spectrum and an estimated surface temperature of around 10000 K in 1900, with a likely radius 16 times that of the Sun, before becoming a B-class star in 1920, then an O-class star in 1940, and finally a Wolf-Rayet star in 1970, with a surface temperature of 95000 K since 1978. It has shrunk to star with a diameter 1.1 times that of the Sun in 1949, then 0.15 times in 1978 and 0.08 times that of the Sun in 1990. AG Pegasi has been described as the slowest nova ever recorded, with a constant bolometric luminosity of the hotter star over 130 years from 1850 to 1980. By the late 20th century, the hotter star has evolved into a hot subdwarf on its way to eventually returning to white dwarf status.Vogel and colleagues calculated the hotter star must have been accreting material from the red giant for around 5000 years before erupting. Both stars are ejecting material in stellar winds. The resulting nebula contains material from both stars and is complex in nature.From 1997 until 2015, AG Pegasi entered a quiescent phase with no further change to its brightness. Then the hot component increased in temperature, which caused the nebulosity around the stars to become more ionised and increase in brightness. The combination of the extremely slow nova and smaller outburst means that Z Andromedae is classed as a symbiotic nova.Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars.
Most of the brighter stars were assigned their first systematic names by the German astronomer Johann Bayer in 1603, in his star atlas Uranometria. Bayer assigned a lower-case Greek letter (alpha (α), beta (β), gamma (γ), etc.) or a Latin letter (A, b, c, etc.) to each star he catalogued, combined with the Latin name of the star's parent constellation in genitive (possessive) form. (See 88 modern constellations for the genitive forms.) For example, Aldebaran in the constellation Taurus (the Bull) is designated α Tauri (pronounced Alpha Tauri), which means "Alpha of the Bull".Bayer used Greek letters for the brighter stars, but the Greek alphabet has only twenty-four letters, while a single constellation may contain fifty or more stars visible to the naked eye. When the Greek letters ran out, Bayer continued with Latin letters: upper case A, followed by lower case b through z (omitting j and v), for a total of another 24 letters. Bayer never went beyond z, but later astronomers added more designations using both upper and lower case Latin letters, the upper case letters following the lower case ones in general. Examples include s Carinae (s of the constellation Carina), d Centauri (d of the constellation Centaurus), G Scorpii (G of the constellation Scorpius), and N Velorum (N of the constellation Vela). The last upper-case letter used in this way was Q.
Bayer catalogued only a few stars too far south to be seen from Germany, but later astronomers (notably Lacaille and Gould) supplemented Bayer's catalog with entries for southern constellations.Carlyle Smith Beals
Carlyle Smith Beals, FRS (June 29, 1899 – July 2, 1979) was a Canadian astronomer.HD 160529
HD 160529 (V905 Scorpii) is a Luminous Blue Variable (LBV) star located in the constellation of Scorpius. With an apparent magnitude of around +6.8 cannot be seen with the naked eye except under very favourable conditions, but it's easy to see with binoculars or amateur telescopes.HD 316285
HDE 316285 is a blue supergiant star in the constellation Sagittarius. It is a candidate Luminous Blue Variable and lies about 6,000 light years away in the direction of the galactic centre.HD 50064
HD 50064 is a blue supergiant located in the constellation of Monoceros, easy to see with small telescopes.HD 64760
HD 64760 (J Puppis) is a class B0.5 supergiant star in the constellation Puppis. Its apparent magnitude is 4.24 and it is approximately 1,660 light years away based on parallax.
The stellar wind structure of HD 64760 has been extensively studied. Its spectrum shows classic P Cygni profiles indicative of strong mass loss and high-velocity winds, but the spectral line profiles are also variable. The variation shows a 2.4 day modulation which is caused by non-radial pulsation of the star itself. Other pulsation periods around 4.81 hours have also been identified.HD 64760 rotates rapidly. Despite its large size it completes a rotation every 4.1 days compared to every 27 days for the sun. This causes the star to be an oblate spheroid, with the equatorial radius 20% larger than the polar radius. It is estimated that the temperature of the photosphere is 23,300 K at the equator and 29,000 K at the poles, due to gravity darkening. In addition, the surface has temperature variations due to its pulsations. The effective temperature for the star as a whole is 24,600 K, to match the bolometric luminosity of 155,000 L☉.HR Carinae
HR Carinae is a luminous blue variable star located in the constellation Carina. It is surrounded by a vast nebula of ejected nuclear-processed material because this star has a multiple shell expanding atmosphere. This star is among the most luminous stars in the Milky Way. It has very broad emission wings on the Balmer lines, reminiscent from the broad lines observed in the spectra of O and Wolf–Rayet stars. A distance of 5 kpc and a bolometric magnitude of -9.4 put HR Car among the most luminous stars of the galaxy.Luminous blue variable
Luminous blue variables (LBVs) are massive evolved stars that show unpredictable and sometimes dramatic variations in both their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of the Large Magellanic Cloud. They are extraordinarily rare with just 20 objects listed in the General Catalogue of Variable Stars as SDor, and a number of these are no longer considered to be LBVs.NGC 2363-V1
NGC 2363-V1 is a luminous blue variable star in the star-forming region NGC 2363, sat the far southwestern part of the irregular galaxy NGC 2366 in the constellation Camelopardalis, near the North Celestial Pole approaching 11 million light years away from our galaxy. It was discovered in 1996 by Laurent Drissen, Jean-René Roy, and Carmelle Robert while examining images taken by the Hubble Space Telescope Wide Field Planetary Camera 2.NGC 2363-V1 is one of the most luminous stars known. It has been undergoing an increase in temperature and luminosity for the last 20 years, after a dramatic increase in its rate of mass loss. Significant luminosity variation within a human lifetime is rare in LBVs, e.g. Eta Carinae during its Great Eruption (1837 to 1855). NGC 2363-V1 shows an extreme B hypergiant spectrum similar to P Cygni rather than the presently cool Eta Carinae outburst spectrum.NGC 6910
NGC 6910 is an open cluster in the constellation Cygnus. It was discovered by William Herschel on October 17, 1786. The cluster was also observed by John Herschel on September 18, 1828. It is a poor cluster and with prominent central concentration, with Trumpler class I2p.
NGC 6910 is the core cluster of the stellar association Cygnus OB9.NGC 6910 is located half a degree east-north east of Gamma Cygni, also known as Sadr. It may be physically related with the nebula IC 1318, which is also known as the Gamma Cygni nebula complex and lies at a similar distance, behind the galactic Great Rift. Cygnus OB9 is located within the Orion arm of the Milky Way. Cygnus OB9's dimensions in the sky are 2.5 degrees by 1.5 degrees, which corresponds at its distance to 175×105 light years across. It includes many OB stars, along with supergiant stars, like the red supergiant RW Cygni. Gamma Cygni is a foreground star, lying at a distance of approximately 1,500 light years. Because it lies behind a number of molecular clouds, the light from NGC 6910 is dimmed by more than one magnitude.The core radius of the cluster is 0.8 parsec (2.6 light years), while the tidal radius is 4.2 parsecs (13.7 light years) and represents the average outer limit of NGC 6910, beyond which a star is unlikely to remain gravitationally bound to the cluster core.
125 stars, probable members of the cluster, are located within the central part of the cluster, and 280 probable members are located within the angular radius of the cluster. The brightest member of NGC 6910 is a blue supergiant with spectral type B2 and apparent magnitude 7.0. It is located at the southeast edge of the cluster. It is also known as HD 194279 or V2118 Cygni and it is a variable star with P Cygni profile. A mag 8.1 star lies at the northwest edge of the cluster and a mag 8.5 O6 giant star (HD 229196 = V2245 Cygni) lies a bit southwest from the line connecting the two brightest stars. Other members of the cluster include two 10.3 mag stars, one being an O9.5 and the other a B0.5 main sequence stars. The star NGC 6910 37 is categorised based on its emission as a Be star and NGC 6910 14 and NGC 6910 25 are beta Cephei variables. In total there are four beta Cephei variables in the cluster, a rather high number. Their presence has been attributed to the higher metallicity of the cluster.Although visible via binoculars, the cluster is too compact to resolve in low power instruments. Individual stars can be seen with 15×100 binoculars. When seen in low magnification through a 5-inch telescope, the cluster looks like a crescent between the two brighter stars, while more powerful magnification reveals more stars forming streams extending to either side of the cluster.Northern Cross (asterism)
The Northern Cross is a prominent astronomical asterism in the northern hemisphere celestial sphere, corresponding closely with the constellation Cygnus The Swan. It is much larger than the more famous Southern Cross and consists of the brightest stars in Cygnus, Deneb, Sadr, Gienah, Delta Cygni and Albireo. The 'head' of the cross, Deneb, is also part of the Summer Triangle asterism.
Like the Summer Triangle, the Northern Cross is a prominent indicator of the seasons. Near midnight, the Cross lies virtually overhead at mid-northern latitudes during the summer months; it can also be seen during spring in the early morning to the East. In the autumn the cross is visible in the evening to the West until November. It never dips below the horizon at or above 45° north latitude, just grazing the northern horizon at its lowest point at such locations as Minneapolis, Montréal and Turin. From the southern hemisphere it appears upside down and low in the sky during the winter months.
In Johann Bayer's 17th-century star atlas, the Uranometria, it was suggested that Alpha, Beta and Gamma Cygni formed the pole of the Christian Cross, while Delta and Epsilon formed the cross beam. The variable star P Cygni was then considered to be the body of Christ. It is believed that KIC 9832227, a contact binary star system located off the right hand 'arm' of the Northern Cross, merged approximately 1800 years ago producing a luminous red nova which is expected to be visible to the naked eye around 2022.R99
R99 (HD 269445) is a star in the Large Magellanic Cloud in the constellation Dorado. It is classified as a possible luminous blue variable and is one of the most luminous stars known.
R99 has a peculiar spectrum that has been described as OBf:pe, "unclassifiable", peculiar WN10, "similar to the unusual LBV HD 5980", "unique", and Ofpe/WN9. The Ofpe/WN9 type remains even though other stars of this type have been reclassified to types between WN9 and WN11. R99 has significant differences to those other stars which preclude it being given a simple WN spectral type: the ultraviolet spectrum is strongly blanketed over a different range of wavelengths; highly ionised iron lines are seen in absorption instead of emission; the Hi lines are unusually narrow and have no P Cygni profile; a lack of any significant absorption features near Hδ; a number of metal lines are unusually strong or weak compared to other stars of the type; there is a small unexplained infrared excess.The wind structure of R99 may be significantly different to most WR stars and LBVs. The normal temperature-stratified WR wind is accelerated to terminal velocity, causing lines of different ionisation levels of Helium to be created at different distances from the star. This does not seem to apply to R99. Significant polarisation of the spectrum continuum is also seen, suggesting an asymmetric wind. This has not been observed in other WR stars.R99 shows brightness variations of about 0.3 magnitude over a period of decades, and smaller amplitudes with the strongest periods at two and ten days. The colour also varies, with the star being bluer at minimum light. It has been classified as a Luminous Blue Variable on account of the variability and spectrum, although it has never been observed in outburst. Others still list it only as a candidate.SN 2011dh
SN 2011dh is a supernova in the Whirlpool Galaxy (M51). On 31 May 2011 an apparent magnitude 13.5 type II supernova (the explosion of a single massive star) was detected in M51 at coordinates 13:30:05.08 +47:10:11.2. It was discovered by Tom Reiland; Thomas Griga; Amédée Riou; and Stephane Lamotte Bailey and confirmed by several sources, including the Palomar Transient Factory. A candidate progenitor has been detected in Hubble Space Telescope images at coordinates 13:30:05.119 +47:10:11.55. The progenitor may have been a highly luminous yellow supergiant with an initial mass of 18-24 solar masses. The supernova appears to have peaked near apparent magnitude 12.1 on 19 June 2011.Emission spectra from W. M. Keck Observatory, obtained by Palomar Transient Factory indicate that this is a type II supernova with a relatively blue continuum with P Cygni profiles in the Balmer series. This is a unique event, because it occurs in a galaxy that is imaged almost constantly. It is expected to be observable for northern hemisphere observers for several months.This is the third supernova to be recorded in the Whirlpool galaxy in 17 years (following SN 1994I and SN 2005cs) which is a lot for a single galaxy. The galactic supernova frequency is estimated to be around one event every 40 years.S Doradus
S Doradus (also known as S Dor) is located 160,000 light-years away, and is one of the brightest stars in the Large Magellanic Cloud (LMC), a satellite of the Milky Way. It is a luminous blue variable and one of the most luminous stars known, but so far away that it is invisible to the naked eye.WR 148
WR 148 is a spectroscopic binary in the constellation Cygnus. The primary star is a Wolf-Rayet star and one of the most luminous stars known. The secondary has been suspected of being a stellar-mass black hole but may be a class O main sequence star.
WR 148 shows a classic WN8h spectrum, but with the addition of weak central absorption on some of the emission lines. NIII and NIV emission lines are stronger than NV, and HeI lines are stronger than HeII, The Balmer series hydrogen lines and some other lines have P Cygni profiles.WR 148 is erratically variable on timescales ranging from seconds to years, but it shows consistent brightness and radial velocity variations with a period of 4.32 days. There is little doubt that it is a binary system, due to the regular variations and the presence of hard x-ray radiation from colliding winds, but the secondary is not clearly detectable in the spectrum. One proposal for a companion that would match the faint absorption features would be a B3 subgiant, but that is not compatible with the orbit. An early calculated orbit based on faint absorption features gave a relatively large mass ratio which imply either a very high companion mass, meaning a black hole, or an unreasonably low primary mass for a luminous WR star. Another analysis of the spectrum finds absorption features consistent with an O5 star, similar masses for the two components, and only a small orbital inclination.Because of its erratic changes in apparent magnitude at so many frequencies WR 148 is classified in the General Catalogue of Variable Stars as a unique type of variable, not a member of any of the defined classes. The shape of the light curve is unusual and has been modelled as being produced by an extended secondary object which may be an ionised cavity in the dense wind of the primary star, produced as the secondary orbits at a distance comparable to the radius of the primary star.WR 148 is found unusually far from the galactic plane for a Wolf-Rayet star, at 500 - 800 pc. Young massive stars such as WN8h WR stars are members of the thin disc population, on average only 60 pc from the galactic plane. It is suggested that WR 148 is a runaway from a supernova explosion. Calculations based on its large peculiar velocity of 197 km/s, current binary orbit, and likely lifetime since any supernova, are consistent with expulsion from a very massive triple system.WR 3
WR 3 is a Wolf-Rayet star located around 16,000 light years away from Earth in the constellation of Cassiopeia.
WR 3 is a member of the nitrogen sequence of WR stars and has a spectrum with strong HeII and NV lines, but weak NIV. HeI lines are very weak or missing, but there are lines of OVI. Unusually, there are lines of hydrogen and absorption components in many lines creating P Cygni profiles. Overall, the emission is weaker than stars of similar spectral type, and it has often been suggested that WR 3 has a type O binary companion. However, there are no other signs of a companion and it is thought to be a single star with a spectral type of WN3-hw. The "h" and "w" indicate that hydrogen is present and the emission is weaker for the class.Ordered by right ascension, WR 3 was the third star in the Sixth Catalogue of galactic Wolf-Rayet stars. WR 1 and WR 2 are also both early WN stars in Cassiopeiae.WR 3 is a massive and luminous star. The presence of hydrogen in its spectrum suggests that it is younger than hydrogen-free WR stars and may still be fusing hydrogen in its core. The emission lines of heavy elements in its spectrum are produced by strong convection and powerful stellar winds rather than complete loss of the outer layers of the star. The wind has been measured at 2,700 km/s leading to mass being lost at four millionths M☉ per year.WR 31a
WR 31a, commonly referred to as Hen 3-519, is a Wolf–Rayet (WR) star in the southern constellation of Carina that is surrounded by an expanding Wolf–Rayet nebula. It is not a classical old stripped-envelope WR star, but a young massive star which still has some hydrogen left in its atmosphere.WR 42e
WR 42e (2MASS J11144550-115001) is a Wolf-Rayet star in the massive H II region NGC 3603 in the constellation of the Carina. It is around 25,000 light years or 7,600 parsec from the Sun. WR 42e is one of the most massive and most luminous stars known.
WR 42e was first catalogued in 2004 as a member of NGC 3603, numbered 954. It was noted as having x-ray and Hα emission. A detailed study published in 2012 showed that the faint red star was actually a highly obscured (6.4 magnitudes in the visual) hot blue Wolf Rayet star and gave it the name WR 42e. Subsequent changes to the naming conventions for new galactic Wolf Rayet stars mean it is also called WR 42-1.WR 42e is located 2.7 arcmin west-northwest of the massive open cluster HD 97950 at the heart of NGC 3603, corresponding to 6 parsecs at the distance of NGC 3603. This is outside the compact core of the cluster where similar massive luminous stars are found. It is speculated that WR 42e was ejected in an unusual three-body encounter possibly involving the merger of two of the stars and the ejection of both the resulting objects.The spectrum of WR 42e shows many characteristics of an OIf* star, such as hydrogen Balmer series absorption lines and emission lines of ionised nitrogen and helium. The relative strengths of the nitrogen emission lines and the lack of absorption in the 468.4 m, helium line indicate a spectral class of O3 If*. However, the Hβ line shows a distinct emission wing. A P Cygni profile for this line is a defining character of the OIf*/WN class and so WR 42e is assigned the type O3If*/WN6.