« back to overview Nebula Load higher resolution (1800 x 1200 Pixel    3500 x 2300 Pixel) Object description
IC 4628 - a part of Gum 55 of the SCO OB 1 star association

Object description:

IC 4628 is a large H-II emission nebula in the constellation Scorpio and is part of the large SCO OB 1 stellar association. It is also popularly referred to as the "Shrimp Nebula". The nebula surrounds the very loose open star cluster Collinder 316 and from its stars it also receives much of the excitation energy that causes the nebular masses to glow red. IC 4628 contains blue reflection nebula components in addition to H-II emission. The stars of Collinder 316 are only a few million years old. The nebular region has a distance of about 5700 light-years to the solar system and covers a size of about 250 light-years.

IC 4628 is the northeastern part of a much larger circular H-II region, which was cataloged as BBW 31100 by a group of South African astronomers (B. Bok, M. Bester, and C. Wade) in the 1950s. Independently, the Australian astronomer Colin Gum published a catalog of H-II regions of the southern sky in 1951, and in it the region is designated Gum 55. As part of Gum 55, IC 4628 is listed as Gum 56. Another catalog designation is RCW 113. The apparent size of GUM 55 is about 5 degrees in diameter.

In the center of Gum 55 is the bright open star cluster NGC 6231, which appears relatively inconspicuous at first glance. The age of the stars in NGC 6231 is estimated to be only a few million years. The number of hot blue stars of spectral class O is given as 15 to 20, whose strong UV radiation excites the whole region to emission. Violent stellar winds are apparently responsible for the ring-like structure of Gum 55, possibly there has been at least one supernova explosion in the vicinity of NGC 6231. The discovery of IC 4628 is based on photographic observations by Edward Barnard.

A wide field view of the whole region around IC 4628 and NGC 6231 we show here and here

High resolution images of NGC 6231 we show here und here

A widefield view of NGC 6231 we show here

A narrowband view of IC 4628 we show here

And a view of IC 4628 taken with a large telescope of ESO can be found at this URL

« Hier or the thumbnail to load a large annoted image and a size comparison to the full moon.

Sun Moon Solar System DeepSky Widefield Miscellaneous Spec. Projects

All Images und all Content are © by Franz Hofmann + Wolfgang Paech