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RCW 75 | Gum 48a

RCW 75 (also known as Gum 48a) is an emission nebula (a large H II region) in the constellation Centaurus. It is located in the southern part of the constellation,midway between the bright stars Hadar and Acrux. The distance to RCW 75 is estimated to be not less than 2,000 parsecs (6,520 light years); This complex appears physically associated with the open cluster Stock 16. The nebulosity would also associated with the reflection nebula vdBH 60, whose four components, indicated with the letters a through d, seem associated with different clusters of infrared radiation sources at distances between 2100 and 2400 parsecs. In the vicinity of the nebula is also the vast nebulous complex Ced 122, visible just to the south, which stretches for some degrees.

Source: https://www.irida-observatory.org/Namibia-Tivoli/RCW_75/RCW_75.htm

This HII region surrounds and is ionised by the young cluster Stock 16, which is part of the Cen OB1 association and contains the reflection nebula complex VdBH 60a, VdBH 60b, VdBH 60c and VdBH 60d. The region is probably physically connected to the huge and diffuse m Cen nebula.

Kharchenko lists 9 ionising members of Stock 16, including the O stars HD 115455 (O8) and DM -61 3587 (O 9.5 V) as well as 7 B-class stars. She gives a distance of 1640 parsecs and an age of 6 million years.

Dutra places the infrared star group [DBS2003] 86 in VdBH 60b at 2400 parsecs and the infrared star group [DBS2003]85 in VdBH 60d at 2100 parsecs.

Avedisova places this nebula in star formation region SFR 306.20+0.18, along with the emission star IRAS 13168-6208 and the dark cloud Dcld 306.2+0.1.

Although the little documented m Cen HII region is named after the prominent G6 II giant m Cen near its core, it is of course ionised by several much hotter OB stars. Avedisova calls this huge diffuse nebula Ge 136 and lists HD 116796 (O9 V) as the main ionising star, along with two B2 class stars. SIMBAD gives an O9 II class for HD 116796 but curiously appears to be missing the surrounding nebula all together.

Source:

http://galaxymap.org/cat/view/gum/48a

1. ^ Turner, D. G. (1985). "The young open cluster Stock 16 - an example of star formation in an elephant trunk?", The Astrophysical Journal, Vol. 292, 148-154. [1985ApJ...292..148T]

 2. ^ Georgelin, Y. P. & Georgelin, Y. M. (1970). "Radial velocities and distances of galactic H II regions.", Astronomy and Astrophysics, Vol. 6, 349-363. [1970A&A.....6..349G]

The RCW Catalogue (from Rodgers, Campbell & Whiteoak) is an astronomical catalogue of Hα-emission regions in the southern Milky Way, described in (Rodgers et al. 1960). It contains 182 objects, including many of the earlier Gum catalogue (84 items) objects.

The later Caldwell catalogue included some objects from the RCW catalogue. There is also some overlap with the Sharpless catalogue-2 (312 items), although that primarily covered the northern hemisphere, whereas RCW and Gum primarily covered the southern hemisphere.

The RCW catalogue was compiled by Alexander William Rodgers, Colin T. Campbell and John Bartlett Whiteoak. They catalogued southern nebulae while working under Bart Bok at the Mount Stromlo Observatory in Australia in the 1960s.

Source: https://www.wikizero.com/en//RCW_Catalogue