Gum 21

Gum 21 is in part a ring nebula surrounding the Wolf-Rayet star WR 14. WR 14 lies at a distance of about 2000 pc. However, there is also significant foreground gas emission, probably associated with the Gum nebula (Gum 12).

Gum 22

This giant star formation region at the boundary of the Vela OB1 association is a blister compact HII region lying just inside the edge of a giant molecular cloud. It is ionised by an enormous star cluster, [BDB2003] G267.92-01.06, that is less than 1 million years old and contains about 2000 stars (about 31 of these candidate O or B class stars). The hottest of these is the O5 class [FP74] RCW 38 IRS 2.

Avedisova adds three more ionising stars: the O4 III giant CPD -47 2963, the O9.5 Ia supergiant HD 78344 and the B0.5 II-Ib CD -47 4551. (SIMBAD gives a cooler O6 class for CPD -47 2963 and says that it is the same star as CD -47 4551.) She places RCW 38 in star formation region SFR 267.93-1.00 with 58 components, including 2 water masers, the supernova remnant CTB 31, at least half a dozen reflection nebulae, the HII regions Gum 22 and Gum 23, and the star cluster Muzzio 1.

A good black and white hydrogen-alpha image of this region can be found here, a Chandra X-ray image of the central cluster here and a MSX 8μm infrared image here.

Gum 23

This giant star formation region at the boundary of the Vela OB1 association is a blister compact HII region lying just inside the edge of a giant molecular cloud. It is ionised by an enormous star cluster, [BDB2003] G267.92-01.06, that is less than 1 million years old and contains about 2000 stars (about 31 of these candidate O or B class stars). The hottest of these is the O5 class [FP74] RCW 38 IRS 2.

Avedisova adds three more ionising stars: the O4 III giant CPD -47 2963, the O9.5 Ia supergiant HD 78344 and the B0.5 II-Ib CD -47 4551. (SIMBAD gives a cooler O6 class for CPD -47 2963 and says that it is the same star as CD -47 4551.) She places RCW 38 in star formation region SFR 267.93-1.00 with 58 components, including 2 water masers, the supernova remnant CTB 31, at least half a dozen reflection nebulae, the HII regions Gum 22 and Gum 23, and the star cluster Muzzio 1.

A good black and white hydrogen-alpha image of this region can be found here, a Chandra X-ray image of the central cluster here and a MSX 8μm infrared image here.

Gum 24

There is little information available in the scientific literature on this mysterious nebula. The Bran catalog identifies RCW 39 with the nebulae Bran 226 and Wray 19-18 and finds two CO clouds with distinct velocities in this direction.

The 3000 parsec distance estimate, if correct, would place RCW 39 in a peculiar isolated location between the Carina arc and the Perseus arm. (Although note that RCW 34 has a similar distance estimate.)

RCW 39 is prominent in infrared, as can be seen in this MSX 8μm image, as well as at radio frequencies as this Parkes image shows.

Gum 25

This HII region appears to be part of the Vela OB1 association and according to Avedisova is ionised by the O9 V star CD -48 4352.

RCW 40 reveals a spectacular bubble structure in this MSX infrared image. This 2MASS infrared image strips away the dust surrounding this nebula and shows the central star cluster.

Gum 26

RCW 42 is a giant HII region and one of the most massive and luminous star formation regions known in the Milky Way. According to Dutra and colleagues, RCW 42 contains the deeply embedded infrared cluster [DBS2003] 38 at a distance of 7100 parsecs. This confirms the location of this nebula either at the outer edge of the Carina arc or in the interarm space beyond this.

One paper argues that RCW 42 lies at the western edge of the immense galactic chimney GSH 277+0+36. The chimney is at a distance of about 6500 pc on the outer edge of the Carina arc, is more than 600 pc in diameter, and extends at least 1000 pc above and below the Galactic midplane.

You can see RCW 42 in this more detailed visual light image and in this infrared MSX image.

Gum 27

This is the planetary nebula NGC 2899 (Gum 27).

Gum 28

Also called NGC 3199, RCW 48 is a ring nebula around the Wolf Rayet star WR 18. Avedisova says that the nebula is also ionised by the B0.5 V star CP -57 2909 and gives a distance of 3160 +/- 500 parsecs. She places RCW 48 in star formation region SFR 283.55-0.98, along with the emission star CD-57 3107, the dark cloud FeSt 2-80 and the nebulae Bran 300B and Bran 300C.

There seems to be confusion about the identification of Bran 300B and Bran 300C. SIMBAD identifies Bran 300B with the star cluster NGC 3247, which Avedisova places in a separate star formation region with RCW 49. SIMBAD identifies Bran 300C with RCW 50, which Avedisova places in a third star formation region separate from either RCW 48 or RCW 49.

According to one paper, WR 18 is moving at a rate of 60 km/s into the gas that makes up the nebula, energising it like an interstellar snow plough. However, this is contradicted by information associated with this recent image of NGC 3199 on the Astronomy Picture of the day website.

Gum 29

This giant HII region and massive star formation region in the Carina arc is associated with the star cluster Westerlund 2. There are two Wolf Rayet stars (WR 20a and WR 20b) as well as at least a dozen O-stars within this massive cluster. The hottest known O-star is the O3 V((f)) MSP 183.

Avedisova places RCW 49 in star formation region SFR 284.22-0.30 along with 4 masers, the smaller nebulae Hoffleit 5, Hoffleit 8 and Hoffleit 11 and the star cluster NGC 3247, which SIMBAD associates with the nebula Bran 300B.

Spectacular views of this region in infrared can be found here and in X-rays here.

A 2007 study gives a distance estimate of 8000 pc +/- 1400 pc.

Gum 30

The HII region RCW 51 surrounds the massive young (8-9 million years) star cluster NGC 3293 and both in turn appear to be located in a similar distance and direction as the giant molecular cloud Sodroski 62. Kharchenko lists 16 ionising B-class stars as probable members, the hottest of which is the B0 Ia supergiant HD 91969. She gives a distance of 2471 parsecs and an age of 8.7 million years. The entire complex lies near the Car OB1 association.

I've sometimes referred to this striking cluster/nebula combination as the Eye of Horus. You can view a more detailed image of the cluster here.