[Placidus (Mike and Trish)]

Originally Posted by IanP

Hi Trish and Mike,

It is very cool indeed, and 1h subs are also COOL ..
S2 is not far away from Ha, so to speak, images in Ha in LMC always produce more data, was there any particular reason why you decided to grab more S2 over Ha

Thanks, Ian. Not sure if by "S2 is not far away from Ha" you mean that they are similar wavelengths (true) or distributed together topographically (sometimes true, sometimes false). Addressing the latter point first, because H is easy to ionize, you get H-alpha in proportion to how much H there is, wherever there is a reasonable source of UV. Conversely, SII has two conflicting requirements to be seen. Firstly there has to be some Sulphur, and therefore old, dredged-up, recycled stuff. But conflicting with that, there needs to be very low gas pressure. You also need very hard UV or shock energy to excite it. Thus in really interesting regions (eg Gabriela Mistral) they are not co-located. In more boring areas, they may be.

Now on to the second question, which is probably what you were getting at. This object is pretty quiet, and therefore pretty sparse in both OIII and SII. Consequently we needed long exposures to see anything at all other than grit. Hope that makes sense.

Originally Posted by Stevec35

Regardless of what it looks like it's a very nice image. Cheers Steve

Thanks, Steve!

Originally Posted by RickS

I don't think I've seen this one before either. Very nice, Mike & Trish!

Thanks Rick. I guess it's not often photographed because it's a relatively quiet area, but it's rather pretty.

Been reading "An Introduction to Galaxies and Cosmology" by Jones MH, Lambourne RJ, and Serjeant S. An accessible undergraduate textbook. They explain how in an area such as around Eta Carinae, the stuff of the galaxy rotates FASTER than the density waves of the spiral arms, like speedboats overtaking a wave, or cars entering a traffic jam. Thus cold gas and dust moves into a star-forming region, and small stars start to form. You see a region a bit like the Dervish. Later, the region starts to produce whopper stars and supernovae, resulting in an OIII-lit cavity like Gabriela Mistral. Finally, you end up with a mature open cluster with no gas left, such as is visible at the extreme bottom left of the Dervish photo.

Best,
Mike