Cygnus (constellation)

Cygnus (the swan) is a constellation in the northern hemisphere that traverses the Milky Way. The arrangement of its main stars means that it is sometimes known as the Northern Cross, in contrast to the southern constellation of the Southern Cross.

Notable features

Constellation Cygnus, AlltheSky.com

Deneb (α Cygni), the constellation's brightest star, occupies one of the vertices of the so-called Summer Triangle. It is a white supergiant of spectral class A2Iae and one of the most luminous stars in the Milky Way, being 54,400 times more luminous than the Sun. In addition, it is the prototype of a group of variables that bear its name, Alpha Cygni variables..

The second-brightest star in Cygnus is γ Cygni, named Sadr, an F8Ib-type yellow supergiant cooler than Deneb but slightly brighter than Deneb. Both Deneb and Sadr are very distant stars, located approximately 1,410 and 1,800 light years from the solar system respectively. The third brightest star is Aljanah (ε Cygni), an orange giant of type K0III twelve times the size of the Sun that appears to be accompanied by a faint red dwarf.

Fawaris, the official name for δ Cygni, is a triple star system with two fairly close components—a bluish-white subgiant B9.5IV and a main-sequence star F1V—and a third further away. Another notable binary is Albireo (β Cygni), one of the most famous double stars in the night sky, composed of a luminous orange giant and a bluish-white main sequence star. For its part, ζ Cygni is a yellow giant of spectral type G8III. Its main interest is that it is a barium star with a high concentration of this element, coming from a companion white dwarf that has been observed with the Hubble Space Telescope at only 0.04 arcseconds from the giant.

61 Cygni, a binary system only 11.3 light-years away, was the first star—excluding the Sun—whose distance from Earth was measured. The system is made up of two orange dwarfs of type K5V and K7V whose average separation is 84 AU. The eccentricity of the orbit, ε = 0.49, causes its separation to vary between 44 AU at the periastrum and 124 AU at the apoastrum. Although there is no consensus regarding the age of the system, it has been estimated at 6000 ± 1 billion years.

Brightness variations (m_v), temperature, radio and symmetric luminosity of χ Cygni

Among the variables of the constellation, χ Cygni should be highlighted, the Mira variable that presents the greatest variation in brightness in a star. Of spectral type S —the brightest of this class—, it has a temperature between 2699 and 3148 K, and a luminosity 6034 times greater than that of the Sun. Between July and August 2005, its brightness reached magnitude 3.8 according to various AAVSO reports, which was its maximum brightness in the last 148 years. Something dimmer is the also variable Mira R Cygni, of variable brightness between magnitude 6.10 and 14.40. On the other hand, X Cygni is a Cepheid whose brightness fluctuates between magnitude 5.85 and 6.91 over a period of 16.386 days.

P Cygni is a star that in 1600 appeared as a third-magnitude body in a place where no star had been observed before. It is a luminous blue variable (VLA) distant 1,560 parsecs, 700,000 times more luminous than our Sun. NML Cygni is a red hypergiant with an estimated size more than 1,100 times that of the Sun, making it one of the largest known stars. Another interesting variable is SS Cygni, the prototype cataclysmic variable of a subgroup of dwarf novae. It is a binary star where the primary is a dense and hot white dwarf, and the secondary is an orange dwarf of spectral type K4. The proximity between the two stars causes the orange dwarf to lose matter from its surface, which becomes part of the of an accretion disk around the white dwarf; the instability of said disk causes the bursts observed in this variable. Likewise, CI Cygni is a symbiotic star composed of a red giant and a white dwarf; After a quiescent period of 30 years, CI Cygni suffered a sharp outburst in August 2008 when its B-band brightness increased by 1.9 magnitudes.

Another notable star in Cygnus is WR 142, a very rare Wolf-Rayet star of spectral type WO. Extraordinarily hot, it has an effective temperature of 200,000 K and is a very compact object, with a radius equal to 40% of the solar radius, despite the fact that its mass is 20 times that of the Sun. Also, within the limits of this constellation is Cygnus X-1, an X-ray source widely accepted as a black hole.

Among the stars with planetary systems is 16 Cygni, a triple system of two yellow dwarfs and one red dwarf; the faintest of the yellow dwarfs has a planet. Gliese 777 is a binary made up of a yellow G6IV subgiant and a red dwarf, two planets having been discovered around the subgiant: the outermost, 1.5 times more massive than Jupiter, moves in an appreciably eccentric orbit (ε = 0.36), while the innermost has a mass 18 times that of Earth. On the other hand, Cygnus is one of the constellations where the Kepler satellite carried out the search for extrasolar planets, finding around a hundred stars with planets. One of the most notable systems is Kepler-11, a yellow dwarf with six planets in orbits. coplanar; the orbital periods of the five innermost planets are less than 50 days, which means that all of them would be included within the orbit of Mercury in our solar system.

Image of NGC 6826 obtained with Hubble space telescope.

The constellation contains two objects from the Messier catalogue. M29 is a 10 million-year-old scattered open cluster that lies at an uncertain distance between 4,000 and 7,000 light-years. M39 is another closer open cluster—it is located about 800 light years away—and has an intermediate age, estimated at 230 - 300 million years. Thirty stars are secure members of the cluster and occupy a volume about seven light-years across.

Cygnus has various nebulae, being NGC 7000, also called the North America Nebula, one of the best known. It is an emission nebula but the exact distance to which it is found - which could be about 1,500 light years - is not known, nor is the star responsible for the ionization of hydrogen that produces the light emission. NGC 7000 and the nearby Pelican Nebula (IC 5070) are part of the same interstellar cloud of ionized hydrogen (HII region). Also the Crescent Nebula (NGC 6888) is an emission nebula, created by the strong stellar wind originated by the Wolf-Rayet star WR 136 that collides and energizes the slower wind that ejected the star when it became a red giant a few years ago. about 250,000 years. Conversely, Campbell's Star is also a Wolf-Rayet star even though it is at the center of a planetary nebula (PK 064+05 1); the approximate age of this nebula is 700 or 800 years. Another planetary nebula is NGC 6826, also known by the nickname "Blinking Eye Nebula", located 2,200 light-years from Earth.

Main Stars

Double star Albireo (β Cygni)

• α Cygni (Deneb), the brightest star of the constellation with apparent magnitude 1.25, is a white-suclid supergiant star. Very far from us, its distance is not known exactly, being between 1600 and 3200 light years. Its brightness is to be extraordinary, with a brightness between 60 000 and 250 000 soles.
• β Cygni (Albireo), with magnitude 3.05, is a double star where the two components, one yellow and the other blue, are separated 34 arcsec. In turn, the first one is a spectroscopic binary.
• γ Cygni (Sadr), the second most brilliant constellation with magnitude 2,23, yellow supergigante at 1500 light years.
• δ Cygni (Fawaris), of magnitude 2,86, a triple star system.
• ε Cygni (Aljanah or Giennah), of magnitude 2,48, an orange giant.
• Cygni, barium star with an accompanying white dwarf.
• Cristian Cygni, orange giant of 3,88 magnitude.
• λ Cygni, multiple star of magnitude 4.75.
• φ Cygni, supergigante orange of magnitude 3,72 located about 1200 light years.
• ο Cygni, denomination shared by two different stars, ο1 Cygni and ο2 Cygni; curiously both are eclipsing binaries.
• ρ Cygni, yellow giant of magnitude 4,00.
• σ Cygni, white-azulada supergiant of magnitude 4,26.
• τ Cygni, multiple star with four components; the main star is a Delta Scuti variable.
• Cygni χ, supergigante type S, whose brightness ranges between magnitude 3,30 and 14,20, the greatest variation known in a star.
• ω1 Cygni, white-azulada subgigante of magnitude 4,94.
• ω2 Cygni (Ruchba), a double star whose observation is very interesting by the contrast between the two components, one red and another blue.
• 11 Cygni, star Be of magnitude 6.03.
• 16 Cygni, a triple system composed of two yellow dwarfs similar to the Sun, and a red dwarf: an extrasolate planet has been discovered around one of the yellow stars.
• 17 Cygni, yellow dwarf of magnitude 4,99 distant 68 light years.
• 29 Cygni, with magnitude 4,96, is a Lambda Bootis star and a Delta Scuti variable.
• 41 Cygni, bright white-yellow giant of magnitude 4,01.
• 52 Cygni, a yellow-orange giant of magnitude 4,22.
• 59 Cygni (V832 Cygni), star system of magnitude 4,74 whose primary star is a Be star.
• 61 Cygni, a binary star formed by two orange dwarfs in the vicinity of the solar system (11.36 light years), one of the best to observe with prismatics.
• P Cygni, bright blue hypergigante star, one of the brightest in the galaxy. Its apparent magnitude is 4.8.
• X Cygni, a strained variable whose brightness varies between magnitude 5,85 and 6.91 in a period of 16,3863 days.

The Campbell Star and the planetary nebula associated with it, observed by the Hubble Space Telescope

• RV Cygni, carbon star and variable semi-regular variable between magnitude 10.8 and 12.4.
• RW Cygni and BC Cygni, large red supergiant.
• SS Cygni, possibly the most observed variable star in the sky, whose magnitude varies between 8.3 and 12.2.
• TT Cygni, carbon star with a dust cover around.
• CH Cygni and CI Cygni, symbiotic stars.
• KY Cygni, a colossal red supergigante, one of the greatest known; its diameter is 1420 times greater than that of the Sun.
• V444 Cygni, an eclipsing binary containing a Wolf-Rayet star.
• V478 Cygni, also eclipsing binary composed of two O-type hot stars.
• NML Cygni (V1489 Cygni), red hypergigant and one of the largest stars known, about 1790 solar radios. Its distance to the Earth is estimated at about 1.6 kpc (about 5500 light years). Discovered by Neugebauer, Martz, and Leighton in 1965, the NML name comes from the names of these three discoverers.
• V1687 Cygni, a massive binary system composed of a blue supergigant and a Wolf-Rayet star.
• HD 184499, star with more than 10 billion years old of magnitude 6.61.

Image of Cygnus X-1 obtained with the Chandra space telescope

• HD 188753, with a possible extrasolar planet; it would be the first discovered around a triple star system.
• Campbell Star (BD+30 3639), central star of the planetary nebula PK 064+05 1.
• A11 and A36, massive stars that are probably part of the star association Cygnus OB2.
• WR 142, very hot and compact Wolf-Rayet star, of the rare spectral type WO.
• BD+40 4210, supergiant blue star and possible luminous blue variable member of Cygnus OB2.
• Gliese 777, binary system where the main component has two extra-solar planets.
• GJ 1245 (V1581 Cygni), triple star system about 15 light years from Earth.
• GJ 1253, dark red dwarf distant 30 light years.
• Cygnus X-1, a binary system composed of a blue supergigante and another massive object, probably a black hole.
• BD+43 3654, supergiant blue star that appears to have been expelled from Cygnus OB2.

Deep Sky Objects

NGC 7000 (north America).

• M29, open cluster that is at an uncertain distance around 6000 light years.
• M39, open cluster at 800 light years distance; the brightest star of the cluster has visual magnitude 6.83 and spectral type A0.
• Nebula North America (NGC 7000), located east of Deneb, its form recalls that of the North American continent.
• Pelican Nebula (IC 5070), whose name is due to the shape similar to this bird.
• Nebula of the Velo NGC 6960, NGC 6992 and NGC 6995, is the rest of an old supernova.
• Mid-Line Nebula (NGC 6888), formed by a Wolf-Rayet Star (WR 136).
• NGC 6826 planetary nebulae (parapadea Eye nebula), NGC 6884, NGC 7027.
• Egg nebula (RAFGL 2688), bipolar planetary protonebulous.
• HB 21 and SNR G067.7+01.8, remnants of mixed morphology supernova.
• Gamma Cygni Supernova Challenge, a distance of about 1700 paras.
• CTB 80, CTB 87 and W63, also supernova remains; the second has compact morphology.
• Galaxy NGC 6946, at the limit with the constellation of Cepheus, where several supernovaes have been observed.
• Cygnus X, a large star-forming region in which some of the brightest stars of the Milky Way are found (e.g. Cygnus OB2 12) and which includes Cygnus OB2, one of the richest stellar associations in the Milky Way, and which is considered by some authors as a young globular cluster.

History and mythology

Cygnus and Lyra.

In Greek mythology, the constellation represented several legendary swans. Thus, Zeus disguised himself as a swan to seduce Leda, from whom, according to one version, Helen of Troy was born.

Orpheus was transformed into a swan after his death, and was said to have been placed in heaven along with his lyre (Lyra).

Finally, it is said that a king named Cycnus was a relative or lover of Phaethon. Apollo's son, Phaethon, tricked his father into allowing him to ride the chariot of the Sun, but he lost control and was struck down by Zeus. After Phaethon's death, Cycnus plunged into the Eridanus River to find him. He did it on so many occasions, that he was transformed into the swan Cygnus, and is visible today in the sky.

On the other hand, Cygnus, together with other constellations in the zodiac sign of Sagittarius (specifically Lyra and Aquila, together with Sagittarius itself), may have a significant role in the origin of the myth of the Stymphalian Birds, one of the twelve labors of Hercules.