RCW nebulae - plug that "gap" in the NGC/IC

[madbadgalaxyman (Robert)]

Some of you will have noticed that there are virtually no NGC/IC emission nebulae plotted in your star atlases for the southern Milky Way between the constellations Ara and Circinus.


Q. Could this be because there are no fairly bright nebulae found between Ara and Circinus?
A. No! There are plenty observable, but they were missed in the NGC and IC catalogues!


Perhaps the most popular catalogue of nebulae in this region of the Milky Way is called RCW, that is:

Rodgers Campbell & Whiteoak.


The RCW is probably the primary designation for fairly obvious nebulae found in this section of the Milky Way, as other catalogues tend to include many nebulae that are ridiculously faint. Despite this, RCW objects are sometimes not plotted in star atlases!


I attach an observing list of RCW nebulae in Ara and Norma, which I assembled from an H-alpha atlas by Georgelin and Georgelin. These objects were selected as being the most prominent nebulae when seen in H-alpha light.


RCWObjects.zip


Perhaps the best example of a very prominent nebula that was missed in the NGC/IC is the easily-observable & extremely large two-degree scale HII region called RCW 108, the small core of which was catalogued as NGC 6188.

(see my recent post in the Deep Sky Imaging section under the NGC 6188 heading)


cheers, madbadgalaxyman

[Paddy (Patrick)]

Thanks for the list and post Robert. I am often a bit puzzled about why some fairly significant DSOs didn't make the NGC or IC catalogues. I recently found this presentation of the RCW catalogue when following up some RCW nebulae in Carina and found it quite interesting and useful. I look forward to exploring your list.

[astroron (Ron)]

Thankyou Robert and patrickome more fodder for observing with the 16" when the weather clears and there is No Moon
Cheers

[madbadgalaxyman (Robert)]

Thanks for the very interesting link, Paddy.

Your link points to a fantastic resource about southern emission nebulae. I know nothing about the accuracy of the information, or about the people involved in this website, but apparently someone obsesses about southern emission nebulae all day and all night! This site is a totally massive data compilation about nebulae.
I can really relate to this obsession..... as I collect and collate galaxies data, for many hours every day!

cheers, madbadgalaxyman

The H-alpha brightness from the Georgelin H-alpha survey that I used for the selection of the most prominent objects in Norma and Ara should be a reasonable indicator of their visual brightness. While the Halpha line is out of range for the eye, objects that are bright in Ha are generally also bright in the [OIII] line that the eye strongly responds to.

[[ On a related issue, plenty of Blue Magnitude 12.5 - 13.5 galaxies were missed in the NGC/IC ; some of them had to wait till the ESO Survey at the end of the 1970s to be discovered ]]