RCW 75, also known as Gum 48A, is a very active HII region fueled by the young star cluster Stock 16 and the OB association of Cent OB1. Numbers of faint stars found just within the eastern boundaries of RCW 75 are suggested to be low-mass pre-main-sequence stars formed from the interaction of the ionization/shock front from RCW 75 with the adjacent gas and dust complex. Stock 16 and RCW 75 otherwise constitute what appears to be a rather passive star-formation complex.
Colin Gum, working at Australia's Mount Stromlo observatory in 1951, completed the first major survey of HII regions visible in the southern hemisphere. He published his nebula catalog in 1955. Although Gum's catalog was largely superceded by the RCW catalog published in 1960 by Alex Rodgers, Colin Campbell and John Whiteoak under the direction of Bart Bok, many HII regions are still referenced by their Gum numbers even today (text adapted from Star Shadows Remote Observatory).
Apo TEC140 (140/f7.2) - FLI Proline 16803 - Ha (240m) R (70m) G (70m) B (120m) - Warrumbungle Observatory, Coonabarabran, NSW, Australia