IC 4628

IC 4628 (also known as the Shrimp Nebula or RCW 116) is a large emission nebula in the constellation Scorpius.

It is observed in the southern part of the constellation, just north of the bright open cluster NGC 6231, which is also located in the same galactic environment; It can be photographed with ease using a telescope and filters suitable for the detection of ionized hydrogen. Its declination is moderately austral, which means that in the northern hemisphere it can only be observed from the medium-low temperate regions.

It is an H II region that directly receives radiation from the massive stars of the Scorpius OB1 association, of which NGC 6231 is the central core. According to a 1984 study, the main ionizing star is the blue giant HD 152723, of spectral class O6; This study also suggests a second star, HD 332417, whose number probably contains an error, since this star is located in another region of the sky. Other sources suggest that the ionizing source is the star HD 322417 (which is probably the same as the one that the 1984 study intended to report), also of class O5 or O6, although this may be located at a greater distance from the Scorpius OB1 region. In the region there are about sixty sources of various kinds, including 19 sources of infrared radiation identified by IRAS and 8 masers, including 5 OH, one water and one methanol; The star Be MCW 1264 (HD 152291), a bright blue giant with strong emissions, would also be associated with the cloud. A 2003 study also identified three young clusters in this region that are deeply immersed in the cloud's gases and therefore emanating infrared radiation; These clusters, the last of which appears to be less rich, are catalogued under the initials [DBS2003] 113, 114 and 117.