As a collector of PNe it was only a matter of time before I tried my hand at M57. It was also an opportunity to try out the new QHY294M camera on a relatively “easy” bright target, although I really want to capture the two outer halos that surround the ring. Of course, I choose the worse possible summer to do this and so it has taken me ages to complete the data collection, and almost as much time to complete the processing of this iconic object.

Imaged with the Edge HD11 and QHY294M PRO camera at prime focus, binned 1x1.

Imaging scale was  approx. 0.33”/pixel, presented at 0.66”/pixel.

Nebula: Astrodon 3nm narrow band filters: 10 hours Ha and N2 and 8 hours for O3 making 28 hours in all combined as

Red = N2, Green = Ha, Blue = O3.

Colours modified using the technique described by Ben’s Astrophotography YouTube video on narrow band processing, step 5:

https://www.youtube.com/watch?v=4A6MxmLlS4Y&list=PLkv07me3-7tL5HFUg3NzVjLCnLFhsMWob&index=6

Stars: Astrodon RGB filters: 30 minutes for red and green, 29 minutes for the blue (1 file got corrupted).

In this image north is (very approximately) to the bottom and right, east is (also very approximately) to the top and right.

One of the interesting things about this object is the difference between what we now believe is its true shape (see https://esahubble.org/images/heic1310c/) and the shape it presents to us on the sky. On the sky we have what looks like a bright ring, with some faint gases filling in the interior. Surround this bright structure and two other rings of material. But what we think we really have is two spherical shells surrounding a thick torus of material that we are looking down on.

This is the bright inner ring that is usually seen. In this region I have chosen to highlight the bright arcs that indicate ionisation fronts that lie within it. This also tends to highlight the knotty structure of this part of the nebula, a feature M57 shares with the Helix nebula. Unfortunately, I don’t have the resolution to show the knots themselves, but rather to suggest their presence!

What appears to be infilling material inside the main ring are lobes of faint gas extending almost directly along our line of sight. Superimposed on this faint gas are some bright linear features, strongest in Ha and darker patches that show up nicely in N2. The whole of the main ring and its inner region is dominated by O3.

Beyond the main ring, O3 emission drops off dramatically and we can see two further halos surrounding the main ring. The inner one gives the appearance of having many rays and bubbles of gas, slightly brighter in N2 than Ha in my image. These rays appear to be associated with features closer to the central star. From a small ground base telescope based in Swindon, UK, these features can only really be hinted at.

The outermost ring is much older than the other two, perhaps around 7000 years old, and is thought to be a spherical shell of material given off during the precursor stars AGB phase. I have tried to indicate its age by deliberately desaturating this part of the image to give it an old, tired look. Its lumpy structure may be due to either the way material was ejected or due to its interaction with the interstellar medium.

The central star has a mass of ~0.65 solar, with a surface temperature of 120,000K and a luminosity 200 solar.
You can read much more about the structure of this object here:

http://simbad.u-strasbg.fr/simbad/sim-ref?bibcode=2013AJ....145...92O

and associated papers.

Clear skies,
Ian