The project

This is a story of a very friendly collaboration between Laurent, a highly skilled planetary photographer, and a deep sky photographer enjoying processing challenges. The idea was to select a project where our skills and equipment would be most profitable and synergistic to achieve a novel result. We thus selected the very peculiar Cat’s Eye planetary nebula. Astrophotographers are of course aware that planetary nebulas have nothing in common with planets, but for this peculiar object, there is something they share. The Cat’s Eye has an extremely bright core, thus enabling us to capture it with the same technique as for planets! At the same time, the outer shell of the nebula is extremely faint, thus requiring very long exposures to detect it. And finally, of course, one needs to combine the very short exposures with the very long ones and use multiple masks to achieve a representative result that can be visually contemplated. All these elements mixed generated a fantastic and exciting cocktail of technical and processing challenges (and this is an understatement!).
To achieve the above, we applied the following strategy:
Laurent generated ~500'000 (!!) images of 200 and 250ms in L and RGB with his C14 edge HD scope at both the native focal length of 3910mm, as well as coupled to a Powermate x2.5 pushing the instrument to a 9750mm effective focal length to resolve the core. He then integrated ~20'000 images of L at 9750mm and ~14'000 images of RGB (color camera) at 3910mm. He also used his C11 scope to obtain a series of Ha and OIII images of the inner and outer shell with exposures of 180s and 600s. From my end, I generated LRGB images at 600s with my SVX180T lens to capture the stars, galaxies and the outer Cat’s Eye shell. The 200/250ms exposures were processed by Laurent using planetary techniques, whereas I took care to process the long exposures with PI and PS. The final composition was processed by combining our skills and points of view.

The final composition

Upon completion of the processing of the core and outer shell, we decided to generate an image showing the full nebula in HOO and to include the core, the stars and galaxies in LRGB. To obtain a more representative vision of the whole nebula, we maintained a near to saturation version of the core, which is extremely bright as compared to the extremely dim regions of the shell. As the core was processed with a planetary imaging technique, we decided to include a magnified version of the core obtained from the 9750mm data, and we adapted the luminosity to better illustrate the colors and contrast nuances.
To our knowledge, this processing scheme enabled us to obtain an unprecedented level of details of the core with non-professional material, and at the same time to show the rings and their structures, as well as the outer shell.

Below, we reported the highlights of the details captured at the core, as compared to the HST image:



1. The Ha discontinuity
2. The central clover
3. The doubling of the filament
4. The asymmetrical intensity of the ring
5.. The tip of the ray

According to our rough estimate, the level of details observed in the core of our image is around 0.3 arcsec, which is of course inferior to what can be achieved on planets such as Jupiter, but considerably superior to classical deep sky astrophotography.

We hope that you will enjoy this result and look forward to any constructive comments/critics.

Nicola & Laurent

About the Cat’s Eye nebula (various sources)

Also known as NGC 6543, the Cat’s Eye nebula is located in the constellation Draco and is approximately 3,300 light-years away from Earth.=MsoNormalAt the heart of the Cat's Eye Nebula lies a white dwarf, which has expelled its outer layers. As revealed by the images from the HST, the nebula exhibits a complex and intricate structure including concentric gas shells, knots, and filamentary structures. The core has an apparent size of 16 x 25 arcsec and shows bipolar outflows, which are thought to be caused by the interaction between the central star’s wind and its previously ejected material. The extended halo, which is around 5 arcminutes across corresponds to material ejected by the central progenitor star during its red giant phase around 85000 years ago.
The Cat's Eye Nebula represents a late stage in the life of a medium-sized star. When the star exhausted its nuclear fuel, it expelled its outer layers, creating the nebula. The multiple shells and rings (which, in 3D are bubbles) seen in the nebula are indicative of several episodes of mass loss. These are ejected by the central star at different times and at varying speeds. The nebula is composed mainly of ionized hydrogen, helium, oxygen, nitrogen, and carbon.
High-resolution images from the Hubble Space Telescope have revealed the intricate details of the Cat's Eye Nebula, showing the fine structure of the concentric shells and the complex inner regions. Observations in the X-ray spectrum have shown that the central star of the Cat's Eye Nebula is emitting X-rays, indicating very high temperatures in the inner regions of the nebula.