Gum 51

Avedisova lists 4 ionising O-stars: the O7 V HD 144918, the O7 V: HD 330386, the O8.5 V HD 144647 and the O9 IV subgiant HD 144900, and gives a distance of 1820 +/- 150 parsecs. She places the nebula in star formation region SFR 332.86+1.85 along the dark globule FeSt 2-212.

The nebula appears to be surrounded by numerous small molecular clouds listed in the [YSM99] catalog and is likely embedded in the compact OB association R105. Humphreys gives a distance estimate of 1580 parsecs for the R105 association. Kharchenko calls this association Nor OB5 and lists the O9 V HD 144695 and 4 ionising B-stars in addition to three of the O-stars mentioned by Avedisova. She gives an age of 12.8 million years and a distance of 1800 parsecs.

RCW 105 has a spectacular bubble structure in infrared, as can be seen in this MSX image.

Gum 52

This bipolar HII region, also called NGC 6164/6165, is associated with the peculiar O-class variable star HD 148937 and is located within the Ara OB1A association.

There are good visual images of this object here, here, and here.

Gum 53

The massive star formation region RCW 108, also called the Rim nebula, NGC 6188, and Gum 53, is ionised by the Ara OB1a association and its core star cluster NGC 6193. Humphreys gives a distance of 1380 parsecs for Ara OB1a.

Avedisova places it in star formation region SFR 336.43-1.26 along with the star cluster NGC 6193, the molecular cloud [TUW2004] SFO 79 and the dark cloud DCld 336.4-01.5.

Kharchenko lists the O7 V multiple star HD 150135 and 3 ionising B-stars in NGC 6193. She gives an age of 7.9 million years and a distance of 1155 parsecs. A 2008 study adds a second O-star to NGC 6193, the ultrahot O3+O6V multiple HD 150136, and gives a distance of 1300 +/- 200 parsecs. The region also contains the infrared cluster RCW 108-IR, which includes a probable O9 class star.

A good black and white hydrogen-alpha image of this region can be found here.

Full colour images are here and here. You can see the MSX infrared image here.

Gum 54a

RCW 110 and RCW 111 appear to be bright spots in the same object, Gum 54.

Avedisova lists two O8.5 V class ionising stars for RCW 110: CD -45 11051 and CD -45 11034, and gives a distance of 2000 +/- 220 parsecs. She places both RCW 110 and RCW 111 in star formation region SFR 340.79-1.01 along with two masers, the star cluster Lynga 14 and the HII region IRAS 16506-4512.

SIMBAD gives a G0 class for CD -45 11051 but this is contradicted by several other papers that support a O8.5 class for this star. (Perhaps G0 is the class of a companion star?) SIMBAD also says that CD -45 11034 is a member of Lynga 14.

The Wolf-Rayet star WR 79b=HD 152386 is located in a similar direction as Gum 54 but has a distance estimate of 2900 parsecs and so may be a background object. On the other hand, a 1999 paper by Benaglia and Cappa says that HD 152386 is definitely associated with Gum 54, but give a quite different O6 Ia f class for this star. They give a photometric distance of 2500 parsecs for the star and suggest a distance of 2800 for an atomic hydrogen (HI) bubble that appears to surround the region.

RCW 110 and RCW 111 appear as one object in this MSX infrared image.

Gum 54b

RCW 110 and RCW 111 appear to be bright spots in the same object, Gum 54.

Avedisova places both RCW 110 and RCW 111 in star formation region SFR 340.79-1.01 along with two masers, the star cluster Lynga 14 and the HII region IRAS 16506-4512.

Dutra and colleagues say that the infrared cluster [DBS2003] 106 is deeply embedded in RCW 111 at a distance of 2600 parsecs.

The Wolf-Rayet star WR 79b=HD 152386 is located in a similar direction as Gum 54 but has a distance estimate of 2900 parsecs and so may be a background object. On the other hand, a 1999 paper by Benaglia and Cappa says that HD 152386 is definitely associated with Gum 54, but give a quite different O6 Ia f class for this star. They give a photometric distance of 2500 parsecs for the star and suggest a distance of 2800 for an atomic hydrogen (HI) bubble that appears to surround the region.

RCW 110 and RCW 111 appear as one object in this MSX infrared image.

Gum 55

RCW 113, also called Gum 55, is a huge region of diffuse nebulosity surrounding the Sco OB1 association and its core ionising cluster, NGC 6231.

Gum notes that this region is "A large roughly semicircular loop, whose ragged appearance is due in part to overlying obscuration. At its centre is the galactic cluster NGC 6231, which is the nucleus of an O-Association".

Humphreys lists 3 O-stars and 27 ionising B-class stars in Sco OB1 and gives a distance of 1910 parsecs.

Kharchenko lists 15 ionising stars for NGC 6231 including 9 O-stars, 5 B-stars and the Wolf-Rayet binary star WR 79. The hottest O-star listed by Kharchenko is the O6 III:(f)p binary giant HD 152233. She gives an age of 6.4 million years and a distance of 1250 parsecs for the cluster. A 2008 study gives a distance of 1640 parsecs and finds 15 O-stars in the direction of the cluster core.

You can find a better view of the bat-like edge of this nebula here and a stunning view of the full RCW 113 nebula and the larger Sco OB1 region here.

You can see the full extent of the vast nebular clouds in the Sco OB1 region in this SuperCOSMOS explorer image and some photographs of SFO 82, the prominent bright-rimmed cometary globule visible inside RCW 113, here. SFO 82 is often called "the Dark Tower of Scorpius" by amateur astronomers and is described in detail in this 1976 paper.

Gum 56

This is IC 4628, the Prawn nebula, which is a dense concentration of gas and dust ionised by the star cluster Trumpler 24. It lies within the more diffuse nebula RCW 113 surrounding the Sco OB1 association.

Avedisova says that the Prawn nebula is ionised by two O-class giants: HD 332417 (O6 III) and HD 152723 (O6.5 III) at a distance of 2100 +/- 200 parsecs. She places it in star formation region SFR 344.22+1.70 with 59 components, including 19 infrared sources, 8 masers, the emission star MCW 1264 and Trumpler 24. (Avedisova misspells the name of the emission star as MWC 1264, but this is clearly an error. The HD catalog gives a completely different location and spectral class for HD 332417 so it appears that Avedisova is mistaken in this case.)

Reed lists the O5 III giant LS 3873=HD 322417, the O6 III giant LS 3868, the O8 star LS 3843, the O9 star LS 3840 and the O9.5 IV subgiant LS 3874 in this direction as well. Given the similarity in names, it seems possible that Avedisova's HD 332417 reference was meant to be HD 322417.

The nebula contains the infrared clusters [DBS2003] 113 and [DBS2003] 114, as well as the infrared group [DBS2003] 117.

This is a black and white hydrogen-alpha image of the Prawn nebula - much more colourful images are widely available on the Internet. You can also see several knots of young star development in this MSX infrared image.

Given the high concentration of O-stars in this direction and the prominence of the Prawn nebula at infrared and radio frequencies, it is surprising that this region has received so little study to date in the scientific literature.

Gum 57

This HII region is a wind blown bubble surrounding the O6.5 Ia supergiant and prominent X-ray eclipsing binary HD 153919. It is in the same direction (but much further away) as the star cluster NGC 6281.

HD 153919 is a runaway star ejected from the Sco OB1 star association in a supernova explosion about 2 million years ago.

You can see the full extent of this huge nebula in this hydrogen-alpha SuperCOSMOS image.

According to SIMBAD, this object is more precisely Gum 57B. Avedisova lists a second ionising star for RCW 119 (the O9 II-III class HD 153426) but SIMBAD says that this is associated with the separate HII region Gum 57A. A 2004 paper concludes that HD 153426 is part of an uncatalogued star cluster at distance of 2100 parsecs.

Gum 58

According to Avedisova, RCW 120 is ionised by the O8 V star CD -38 11636 and the B2 V star VDBH 84B. She places the nebula in the star formation region SFR 348.26+0.47 along with 3 masers and the radio HII region [CH87] 347.386+0.266.

A 2005 study refers to the Avedisova paper and gives the class of the main ionising star as O6 V, so CD -38 11636 may be hotter than Avedisova suggests.

You can view an interesting multiwavelength image of RCW 120 and see the Spitzer infrared view here.

Gum 59a

RCW 121, RCW 122 and RCW 123 are probably ionised by stars in the Havlen-Moffat 1 cluster. There is a large and very uncertain range of distance estimates for the objects in this direction, from 2000 to 5000 parsecs.

RCW 122 separates into at least two distinct sources in infrared. The brightest one by far is IRAS 17167-3854, which is sometimes further subdivided into RCW 122A and RCW 122B. Dutra and colleagues locate the infrared cluster [DBS2003] 119 in this direction at 2000 parsecs. A distinct smaller nebula to the northwest in galactic coordinates is IRAS 17158-3901, also known as RCW 122C. These sources are ionised by several O-stars, including one as bright as O4.

A 2008 paper concludes that RCW 121 and RCW 122 are embedded in a 1.2 million solar mass molecular cloud and both nebulae are likely ionised by several O7 V class stars with a distance of about 5000 parsecs.

The larger region around RCW 121, RCW 122 and RCW 123 is spectacular in infrared. This Spitzer image shows only a part of this region. While not as detailed, this MSX image shows a wider view of the region in which the compact HII regions RCW 121 and 122 are seen to be bright knots at the rim of a vast star forming cavity centred on the ionising cluster Havlen-Moffat 1 and filled by the diffuse HII region RCW 123.

Gum 59b

RCW 121, RCW 122 and RCW 123 are probably ionised by the cluster Havlen-Moffat 1. The large diffuse nebula RCW 123 is in the same direction and almost the same distance as WR 89 in the cluster Havlen-Moffat 1.

The RCW catalog cross references this object with the Sharpless object E6 = Sh 1-6 = Sh 2-5. The locations given for Sh 2-5 and RCW 123 differ considerably but this is not surprising because this is a huge diffuse nebula. The RCW catalog further notes that this object is a "Loop".

This large scale SuperCOSMOS image confirms that Sh 2-5 and RCW 123 are different locations within a huge diffuse nebula prominent in hydrogen-alpha.

The larger region around RCW 121, RCW 122 and RCW 123 is spectacular in infrared. This Spitzer image shows only a part of this region. While not as detailed, this MSX image shows a wider view of the region in which the compact HII regions RCW 121 and 122 are seen to be bright knots at the rim of a vast star forming cavity centred on the ionising cluster Havlen-Moffat 1 and filled by the diffuse HII region RCW 123.

Gum 60

This is NGC 6302, the Bug nebula. You can see an amazing Hubble image of this planetary nebula.