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.
You can view a larger image of RCW 75 here
and the full extent of the nebulosity (including the huge diffuse m Cen nebula) in this SuperCOSMOS hydrogen-alpha image
. You can also see RCW 75 at the edge of the far larger (and twice as distant) RCW 74 nebular complex in this Spitzer infrared image
This HII region surrounds and is ionised by the young (3-5 million year) cluster Stock 16 which is associated with the OB association Cen OB1. The area also probably includes the adjacent m Cen nebula.[1
The m Cen nebula is entry 136 in Georgelin and Georgelin's nebula catalog. [2
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,