The Seagull Nebula (IC 2177) is a large region of nebulosity located approximately 3,650 light-years away in the constellation Monoceros (the Unicorn), on the border with Canis Major. The nebula includes an H II region, open star clusters, dark dust clouds, and reflection nebulae.
The Seagull Nebula has an apparent size about seven times that of the full Moon. It was named the Seagull because its complex of dust and gas forms a shape reminiscent of that of a seagull in flight.
The nebula is composed of interstellar dust clouds and hydrogen, helium, and other gases that are ionized by the energetic young stars formed within the nebula. The radiation of the new stars causes the surrounding hydrogen gas to glow with a reddish colour in long-exposure images.
The light of the hot blue OB-type stars is also reflected off the tiny dust particles in the nebula’s clouds and it creates patches of reflection nebulosity that contrast with the red emission nebula.
The Seagull Nebula complex is home to dozens of massive OB stars and reflection nebulae, as well as to several embedded young clusters. It is part of the larger star-forming region CMa R1, which is the most prominent feature of the Canis Major OB1 association.
The CMa OB1 association may include more than two dozen star clusters that appear in the same line of sight. It is uncertain which ones are physically associated with the group. The open cluster NGC 2353 was once believed to form the core of CMa OB1 but is now believed to be too young to be a member. The same goes for NGC 2343, NGC 2335, and NGC 2323.
IC 2177 surrounds the star HD 53367, which lies in the Seagull’s head and appears as the Seagull’s eye. The strong ultraviolet radiation from the brilliant young star makes the surrounding nebula glow.
The star is in fact a triple star system whose primary component is a young variable Herbig Ae/Be star – a massive pre-main sequence star – of the spectral type B. The star has a mass more than 12 times that of the Sun and is 11,000 times more luminous than the Sun.
The star has a spectroscopic companion at a separation of only 1.7 astronomical units (Earth-Sun distances). The companion was discovered in 2006. The two stars have an orbital period of 367.7 days. They orbit each other at an angular separation of 2.6 – 2.7 milliarcseconds.
The double star system has a companion, another Herbig Ae/Be star, separated by only 0.6 arcseconds from the main pair. All the components are believed to be members of the CMa OB1 association.
The head of the Seagull is a compact cloud that has its own designation in the New General Catalogue, NGC 2327. The nebula is catalogued as Sh2-292 in the second Sharpless catalogue of HII regions (1959). It was the first object catalogued by Australian astronomer Colin Gum in his catalogue of emission nebulae located in the southern sky. It has the designation Gum 1 in the Gum catalogue.
The Seagull’s head is both an emission and reflection nebula. Most of its light is emitted by the gas ionized by newly formed stars, but some of it is also reflected off the stars outside the nebula.
The dark dust lanes that give texture to the nebula’s glowing regions are formed of denser material. They conceal some of the brighter portions of the nebula.
The small knot at the tip of the Seagull’s wing is an emission nebula catalogued as Sh2-297, while the smaller nebula near the Seagull has the designation Sh2-295.
Sharpless 2-297 is illuminated by the 8th magnitude star HD 53623, a hot blue giant or bright giant of the spectral type B1II/III. The nebula contains many young stellar objects, including one with a mass of 5.4 solar masses and an extended envelope that weighs between 30 and 40 solar masses.
The wings of the Seagull are formed by an H II region catalogued as Sharpless 2-296. The wings span 100 light-years across. The star-forming region contains red glowing material and dark lanes of dust. It is the birthplace of new stars. Some of these stars are visible in optical images while others are still shrouded in their parent clouds. They excite the surrounding clouds, causing them to glow. The stars also shape and sculpt the clouds by exerting pressure on them.
The binary star FN Canis Majoris is the brightest star in Sh2-296. It is a massive runaway star that speeds through space and produces a bow shock as its stellar winds interact with the interstellar medium.
The brighter component in the FN CMa system is a B-type star that shines at magnitude 5.69. The star has an estimated mass between 19 and 36 times that of the Sun. The companion is fainter, with an apparent magnitude of 7.04. The system is only 6 million years old.
The Seagull Nebula was discovered by the 19th-century Welsh amateur astronomer and astrophotographer Isaac Roberts. The German-born British astronomer William Herschel had spotted a small bright clump in the nebula in 1785, but the rest of the nebula was discovered photographically by Roberts about a century later.
The Seagull Nebula lies along the imaginary line extended from Sirius to Procyon. It appears northeast of the magnitude 4.08 orange giant Theta Canis Majoris, the star marking the Great Dog’s nose. Most of the nebula lies in the constellation Monoceros, but a part of one of the Seagull’s wings is located in the neighbouring Canis Major.
Sirius, the brightest star in the night sky, can be found by extending the line formed by the three stars of Orion’s Belt to the southeast. Sirius forms a bright, conspicuous asterism known as the Winter Triangle with Procyon and Betelgeuse. Theta Canis Majoris is the brightest star just northeast of Sirius.
The Seagull Nebula lies in the same area as the smaller Thor’s Helmet Nebula (NGC 2359), an emission nebula 11,960 light-years away in Canis Major. The two nebulae appear in the same wide field of view in small telescopes. Thor’s Helmet is illuminated by the Wolf-Rayet star WR7, an exceptionally hot star that will soon meet its end in a brilliant supernova.
Seagull Nebula – IC 2177
|Constellation||Monoceros, Canis Major|
|Right ascension||07h 04m 25s|
|Declination||−10° 27′ 18″|
|Distance||3,650 light-years (1,120 parsecs)|
|Names and designations||Seagull Nebula, IC 2177, Gum 1, Sh2-292, LBN 1027, PKS 0702-103, PKS J0704-1027, VDB 93, RCW 2, RRF 2486|