P Cygni

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P Cygni
Observational Data
Designation 34 Cygni
Nova Cygni 1600
P Cyg
HD 193237
HIP 100044
Right ascension 20h 17m 47.2020s[1][2]
Declination +38° 01′ 58.5527″[1][2]
Constellation Cygnus
Type of object Hypergiant
Magnitude Apparent Mag: +4.77[3]
Absolute Mag: -6.65 / -7.70[3]
Distance from Earth 10192.60 ly[3]
Radial velocity -8.90 ± 0.8 km/s[1][4]
Proper motion RA: -3.18 mas/yr[1][2]
Dec: -6.45 mas/yr[1][2]
Parallax 0.32 ± 0.16 mas[1][2]

P Cygni (34 Cygni, Nova Cygni 1600, P Cyg, HD 193237, HIP 100044) is a hypergiant variable star in the constellation of Cygnus, the swan.[5] The star is known for being the third variable star discovered as well as one of the brightest.[6] It is the prototype for a class of stars known as "P Cygni" stars, which have distinctive emission lines and blue shifted absorption lines.[7]

Willem Janszoon Blaeu (a Dutch astronomer) was the first person to notice the existence of a new star on August 18, 1600.[8] It appears at the third magnitude for several years before fading to below unaided eye visibility. However it returned to its former brightness in 1626 as well as 1655. Since the 1670s, it has been just about visible to the unaided eye with a magnitude of five, though dark skies are required. The star was named by Johann Bayer using his standard designation method.

Properties and Structure

P Cygni is situated 10192.60 light years from Earth.[3] The star has mass between 50-60 solar masses and an extremely hot surface, estimated to have a temperature in excess of 19,400 kelvin.[5] This high temperature means it radiates somewhere between 500,000 to 900,000 times more energy than the Sun.[5] This puts its absolute magnitude at around -8.9, making it one of the brightest stars in the galaxy.[9] However our view is slightly dimmed by an intervening cloud of gas and dust. The star is thought to be losing mass in the form of an intense stellar wind traveling at 300 km/s.[5] It is estimated to loose three hundred thousandths of a solar mass per year, which is three million times more mass than the Sun looses in its own Solar wind. This complicates the observation of the star as light must pass through this wind on its way to Earth and the particles in the wind interfere with the light.

The star's brightness continues to change, increasing by around 15% per century caused by a reduction of the star's temperature by 6% per century.[5] Although this means the total energy radiated by the star is reduced, it means less is emitted in the ultraviolet and instead radiated in the visible. There are still small fluctuations up and down, though only at most by 0.2 magnitudes.[8] These variations can generally occur with a period of 0.156 days or 3.75 hours, though they can be fairly irregular and are thought to be due to possibly pulsation or flares on the star's surface.[3] P Cygni's fluctuation history place it in a very exclusive group of variable stars known as S Doradus star. Other members include Eta Carinae and S Doradus in the Magellanic Clouds.


  1. 1.0 1.1 1.2 1.3 1.4 1.5 P Cygni. Simbad Astronomical Database. simbad.u-strasbg.fr. Retrieved on December 29, 2021.
  2. 2.0 2.1 2.2 2.3 2.4 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics 474 (2): 653-664. doi:10.1051/0004-6361:20078357. Bibcode2007A&A...474..653V.  arXiv:0708.1752
  3. 3.0 3.1 3.2 3.3 3.4 P Cygni (34 Cygni) Star Facts. universeguide.com. Retrieved on December 29, 2021.
  4. Gontcharov, George (2006). "Pulkovo compilation of radial velocities for 35495 stars in a common system". Astronomy Letters 32: 759-771. doi:10.1134/S1063773706110065. Bibcode2006PAZh...32..844G.  arXiv:1606.08053
  5. 5.0 5.1 5.2 5.3 5.4 Jim Kaler (September 13, 2003). P Cyg. stars.astro.illinois.edu. Retrieved on December 29, 2021.
  6. David Darling. P Cygni profile. daviddarling.info. Retrieved on December 29, 2021.
  7. Ian Czekala (January 26, 2011). The Variability of Massive Stars. astrobites.org. Retrieved on December 29, 2021.
  8. 8.0 8.1 Matthew Templeton. P Cygni. aavso.org. Retrieved on December 29, 2021.
  9. P Cygni. spider.seds.org. Retrieved on December 29, 2021.