Hello,

Well, it's been a while since my last image. I finally got fed up with the QHY294 and replaced it with an ASI2600M Pro. At the moment I haven't changed from my 1.25" Astrodon filters so this image is cropped to remove the vignetting. The APS-C size camera is also revealing a few reflections at the edge of the field that I've yet to find the cause of, so they've been cropped out as well. I will also need to properly sort out the backspacing for the Edge, which I've been able to avoid so far with the smaller sensors that I've been using up till now. But, despite these issues, I am a lot happier with this camera than the 294.

This is an image of M4-17, also known as PN G079.6+05.8. In this image north is (approx.) to the top and east is (approx.) to the left.

The stars were taken using the broadband filters, M4-17 and the background nebulosity are both narrowband, using Ha, N2 and O3 filters.The colour combination is complex! The following formula where used:

• Red:  N2+Ha*(1+HN_mod)
• Green: (0.2*Ha+2*O3)*(HO_mod)
• Blue: 2*O3

Where HN_mod = Ha*N2 and HO_mod = Ha*O3

The idea is that in red the Ha is boosted where there is both Ha and N2 and the green signal is modified according to the presence of both Ha and O3. I’m trying to use the technique described by Adam Block in his narrow band image of the Rosette nebula (Sep 2022). I’m not entirely sure how well I’ve succeeded. The upshot is that where you have Ha and N2 you get orange, Ha and O3 comes out slightly mauve and where there are all 3 you get an enhancement of the Ha and N2 knots as can be seen in the wings. There is little difference between the Ha and N2 images.

M4-17 has a bipolar structure, with a well-defined ring. The size of the ring is 20”, with the total major axis being 31”. 

An expansion velocity of 17.5 km/s and a distance of 7175 light years suggests that this planetary is 7160 years old.

There are various studies concerning molecular abundances which include M4-17 (e.g. HCN and HCO+ in Planetary Nebulae: The Next Level by D.R.Schmidt, et al, March 2022) and it is often included in surveys of nebulae, but there doesn’t appear to be any detailed study of this little PNe.

The bipolar outflows (which I think of as the “wings”) are much dimmer than the main ring. And much of the surrounding nebulosity is dimmer still. This image is a composite of 4 different versions of the same set of master integrations: stars only, and then starless versions highlighting the nebulosity, the wings and the ring. Each was processed separately before being combined into the single image you see here.

The region is full of nebulosity. I haven’t been able to identify the large cloud of gas to the west (left hand side of the image), but it appears to be part of the same complex as the one NGC6888 (~5.5 degrees south) is embedded in. The nearest I know of are LBN 260 and LBN 262, but these are too far west. This nebulosity shows up in both Ha and N2, although the Ha is stronger, hence the orange colour.

I quite like the idea that this image shows the dying embers of M4-17, scattering material back to the ISM where perhaps one day it will be incorporated into the surrounding nebulosity and be reborn (phoenix like) as a new stellar system.

Cheers,
Ian