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IC 4628 - the Prawn Nebula and Collinder 316 in a wide angle view
 

 
Description of object:

A mosaic of IC 4628, Collinder 316 and NGC 6231

Our image shows a mosaic, consisting of 2 exposures, from IC 4628 (also cataloged as GUM 56) to the open star cluster NGC 6231 in the constellation Scorpio. The mosaic appears slightly reddish, but this is due to the large and extremely faint H-II region BBW 31100 overlaying the entire image.

IC 4628 is a very large star forming region with a diameter of about 250 light years and belongs to the Sco OB1 association. This H-II region is only a part of a much larger, very faint, region whose center is the open star cluster NGC 6231. It is cataloged as BBW 31100 or GUM 55, and RCW 113 is a part of it. The total apparent size of BBW 31100 is given as 6 x 6 degrees. The entire region lies at a distance of about 6000 light years from the solar system. IC 4628 also bears the popular name of the Prawn Nebula. The H-II region was discovered by Edward Barnard. Translated with www.DeepL.com/Translator (free version)

NGC 6231 appears rather unspectacular at first sight, but this is wrong. It is one of the brightest open clusters in the southern sky. It contains up to 15 extremely hot, blue stars of spectral class O, whose strong UV radiation ionizes the surrounding hydrogen gas and makes it visible. The stars are extremely young, believed to be only around 5 million years old. It has a diameter of about 25 lightyears and is classified according to Trumpler as type I 3 p. The cluster contains at least 3 Wolf-Rayet stars. It was first described in 1654 by Giovanni Battista Hodierna. Hodierna was an Italian naturalist and a student of Galileo.Translated with www.DeepL.com/Translator (free version)

 
Trumpler 24 and Collinder 316 are also very young open star clusters, formed from the hydrogen gas masses of IC 4628.

NGC 6268 is an open star cluster, classified as type II 2 p by Trumpler. Its distance is given as 3500 light-years. NGC 6268 was discovered by the Scottish astronomer James Dunlop on June 5, 1826.
NGC 6264 is an open star cluster, classified as type I 3 m by Trumpler. Its distance is given as 3700 light-years. NGC 6242 was first described by Nicolas Lacaille in 1751.
NGC 6192 is an open star cluster, classified as type I 2 p by Trumpler. Its distance is given as 5000 light years. Because of its distance NGC 6192 could be a part of the Sco OB1 association. NGC 6192 was discovered by James Dunlop on May 13, 1826.


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Zeta 1 and Zeta 2 Scorpio

The two stars do not form a binary system and just happen to be close together. Zeta 1 is a blue giant star, about 100 times larger than the Sun. It is cataloged as a spectral type of class
B1 and is part of the Sco OB1 association. Zeta 2 is of spectral type K5 and is much closer to the solar system at a distance of about 150 light years and is therefore not part of the Sco OB1 association.
 
The cometary globules Dcld 343+2.8

Dcld 343+2.8 - with the popular name "the dark tower" - is a part of GUM 55. The head of the globule points towards the open star cluster NGC 6231. Numerous young and hot stars nearby ionize the front part of the molecular cloud and produce a red emission nebula edge. In addition to the emission regions, five small reflection nebulae are visible in the globule.


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A detailed, deep image of Dcld 343+2.8 can be find here.

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