Delphinus (constellation)

Delphinus (the dolphin), is a small constellation in the northern hemisphere very close to the celestial equator. It was already included in Ptolemy's list of 48 constellations and also forms part of the modern IAU-approved list of 88 constellations.

Delphinus looks like a jumping dolphin and can be easily recognized in the sky. It is surrounded by Vulpecula (the fox), Sagitta (the arrow), the eagle (Aquila), the zodiacal constellation of Aquarius, the little horse Equuleus and finally by Pegasus, the winged horse. Another way to recognize it is by having a shape similar to that of a kite and by being small.

Notable features

Constellation of Delphinus, AlltheSky.com

Although the stars in this constellation are not among the brightest in the sky, Delphinus contains several binary stars of interest, including β Delphini (called Rotanev) and α Delphini (Sualocin), the two brightest in the sky. constellation. Rotanev is composed of a giant of the spectral type F5III and a white-yellow subgiant of type F5IV. They complete an orbit around the common center of mass every 26.66 years and the distance between the two stars fluctuates between 8 and 18 AU. For its part, the main component of Sualocin has a spectral type B9, being a main sequence star or a subgiant that has just begun to evolve. It is accompanied by a white main-sequence star with an orbital period of 17 years, which is itself a spectroscopic binary with a 30-day orbit.

ε Delphini —officially called Aldulfin— is the third brightest star: it is a bluish-white subgiant of spectral type B6IV with a surface temperature of 13,700 K and a luminosity 676 times that of the Sun. γ Delphini is another binary composed of an orange subgiant of type K1IV and a yellow dwarf of type F7V. The two components move in a markedly eccentric orbit (ε = 0.88) with a separation that varies between 40 and 600 au, being its orbital period of 3249 years. δ Delphini is also a binary—two identical but slightly hotter yellow-white subgiants than those in the Rotanev system—with a short orbital period of only 40.58 days, its duplicity having been detected by spectroscopy.

Among the variables of the constellation is R Delphini, a Mira variable whose brightness oscillates between apparent magnitude +7.6 and +13.8 over a period of 285.07 days. Another variable to highlight is U Delphini, a red giant of type M4-6II-III with a bolometric luminosity —in all wavelengths— 10,000 times greater than that of the Sun; its spectrum shows the presence of technetium, an element of the s-process produced by stellar nucleosynthesis. EU Delphini, a type M6III pulsating giant whose variability was detected by Thomas Espin in 1895, has similar characteristics. By contrast, W Delphini is an eclipsing binary composed of a primary component of spectral type A0e or B9.5Ve and a secondary component of type G5IV; its orbital period is 4.8061 days.

Image of the NGC 7006 cluster obtained with the Hubble telescope

There are several stars in the constellation that have planetary systems. 18 Delphini (Musica) is a yellow giant of type G6III whose planet, named Arion by the IAU, has a mass at least ten times that of Jupiter. HD 195019, also a binary, has a "hot Jupiter" planet revolving around the main component of the system, a yellow dwarf or subgiant. Another star with a planet is HD 196885; the latter's estimated mass is three times that of Jupiter and it moves 2.6 AU from the star.

Among deep-sky objects, Delphinus includes two globular clusters, NGC 6934 and NGC 7006. The first of these is 52,000 light-years away and follows a highly eccentric orbit through the Milky Way along an orbital plane inclined 73° to the galactic plane. Similarly, NGC 7006 is part of the galactic halo and also has a very eccentric orbit around the center of the galaxy, which suggests that it could have formed in a small galaxy other than ours that was later captured by the Milky Way. It is 135,000 light years from Earth.

The constellation has two planetary nebulae, NGC 6891 and NGC 6905. According to measurements made by the space probe Gaia, they are located at 7470 and 7620 light-years respectively. The central star of NGC 6891 is of type O3Ib(f*) and has a temperature of 50,000 K. The central star of NGC 6905 is a Wolf-Rayet star of type WCE and 141,000 K in diameter. temperature.

Main Stars

• α Delphini (Sualocin), of magnitude 3,8, multiple star of seven components; only two of them form a true star system.
• β Delphini (Rotanev), the brightest constellation with magnitude 3,6, is equally a multiple star of five components, although only two of them are physically related.
• γ Delphini, one of the most studied binary stars composed of an orange subgigante and a yellow dwarf. They can be solved with a small telescope, constituting an interesting object for the astronomer of color contrast.
• δ Delphini, variable star of magnitude 4,43. Along with the previous three forms asterism called the coffin of Job.
• ε Delphini (Aldulfin or Deneb Dulfim), white-smoothed star 3,95, the third brightest of constellation.
• γ Delphini, white star of the main sequence of magnitude 4.68.
• Cristian Delphini, white subgiant of magnitude 5.39.
• θ Delphini, distant orange supergigante of magnitude 5.70.
• ι Delphini, equally a white star of the main sequence although of magnitude 5.42.
• κ Delphini, yellow subgiant of magnitude 5.07.
• ρ Aquilae, despite his name belongs to the constellation of Delphinus, to which he crossed from Aquila in 1992. Its magnitude is 4.94.
• 13 Delphini, bright white star of the main sequence of magnitude 5,61.
• 15 Delphini, double star of magnitude 6.01.
• 16 Delphini, white star of magnitude 5.54.
• 18 Delphini, a yellow giant with an extrasolar planet.
• R Delphini, variable type Look variable between magnitude 8.3 and 13,3 with a period of 285 days.
• U Delphini, red giant and semi-regular variable whose main period is about 1200 days.
• W Delphini, eclipsing binary of magnitude 9,69.
• TY Delphini, of magnitude 9.7, is also an eclipsing binary.
• EU Delphini, also red and semi-regular variable giant with a period of 59.7 days.
• LS Delphini, contact binary of magnitude 8,65.
• MR Delphini, a triple system that is also an eclipsing binary.
• HD 194598, star from the galactic halo of very low metallicity.
• HD 195019, binary star with an exoplanet of the type "hotjupiter".

Planetary nebula NGC 6891

• HD 196885 (HR 7907), yellow subgigant with an extrasolate planet.
• WASP-2, distant orange dwarf with a planet of the type "hotjupiter".

Deep Sky Objects

• Planetary nebulae NGC 6891 and NGC 6905. In the first one, the central star is 12.5.
• NGC 6934, globular cluster of magnitude 9.75. It was discovered by William Herschel on September 24, 1785.
• NGC 7006, also a globular cluster of magnitude 12. Distant 135 000 light years—five times the distance between the Sun and the center of the galaxy—is part of the galactic halo.
• NGC 7025, spiral galaxy at 210 million light years.

Mythology

The constellation of Delphinus represented at John Flamsteed's Atlas Coelestis.

According to Germanicus, Caesar, in his Latin version of the Phaenomena of Arato de Solos,^{[citation required]} and Eratosthenes of Cyrene, in his Catasterisms (καταστερισμοί), among others, the famous Nereid Amphitrite she agreed to marry Poseidon—from whom she had tried to hide—once she was found among the islands of Atlantis by Delfino, a dolphin sent by Poseidon, who was so grateful for it that he decided to place it among the stars.

He can also be identified with Arion of Lesbos who then threw himself into the sea and miraculously managed to reach the coast of Laconia riding on the back of a Dolphin. He did this to escape some rogues tried to kill him aboard a Corinthian ship to try to keep his money.