GC 7293 Helix-Nebula Structure in OIII/Ha – A Novel View!

After reading the article cited below, I decided to give the OIII/Ha rendering idea a try as a couple of my previous postings attest. But the known complexity of the Helix nebula seemed ideal for this, but the only images I had that were appropriate were some from 2019 taken with a somewhat crappy camera on TAO150 Deep Skies West (South). Shortly after this image was gathered, they replaced the camera…but, no help to this endeavor!

One thing I did that Guerrero, et al. did not do is I extricated the Ha and OIII pure emission lines from their continuum background. For this, I used a script I wrote (and documented) that can be obtained at this Dropbox link: https://www.dropbox.com/sh/9vfssnx7n2n6ydr/AAAnTU7cylp-5efJE2AT27d7a?dl=0 .

This image was processed hard, in terms of contrast, to bring out fine-scale variations and structures, at the cost of the gentle fogginess of clouds, often portrayed in nebula pictures, being absent.  Furthermore, I isolated the nebula (as best I could) to keep the background from being strongly processed and detracting from the image subject. (I.e., the regions beyond the core nebula have been blurred intentionally.)

With those caveats, Hope you find the technique and result interesting and informative. Notice, for instance, the radial streamers (“comets”) around the center that, on the left, become tangential. This suggests that the outflow is impeded by some background gas, perhaps. However, some radial flow occurs sporadically around the edge, perhaps indicating locations with a less dense or absent prevailing nebula.
Between the radial and tangential strands on the image’s left, lies a region of disorder, probably caused by turbulence as the outward flow is slowed by gases piling up behind the leading shock.
The faint lobe on the right (pretty much blurred out here), and maybe the one on the left as well, suggests to me NGC 7293 may be a bipolar (two-lobed) nebula, much like the Butterfly Nebula, that we are viewing down the long axis. (The lobe on the right has radial structures too, that are not revealed in this intentionally blurred rendition. See image B for those structures.)

BTW, 1 pixel on my image spans nearly 9 billion kilometers at the location of the Helix Nebula! The fine details are anything but small structural elements!

Alex Woronow


1.    “Unveiling Shocks in Planetary Nebulae”, M.A. Guerrero, et al. (2013)