Helix faint features: One photon per pixel every four hours
Trying to get the absolutely faintest outer shock fronts in the Helix, we stacked 16 hours in one-hour 2x2 binned subs, taken over this last new moon.
The faint thin shock fronts coming to a point at the extreme left of the photo were about 6 counts above background in the stacked image. That's about 9 photo-electrons. At 50% photon efficiency, that means that about 18 photons hit each relevant 2x2 binned pixel over 16 hours. That's about one photon per unbinned pixel (0.55 sec arc) every four hours! The brightest nebular features of the "eye" are about 360 times brighter.
We've previously tried this using 30 hours of unbinned subs, or 10 hours of 30 minute 2x2 binned subs, and gotten nowhere near the same result. Nothing to show.
The image is 30% full size, but these features are so faint that looking at them full size doesn't tell you much more. Wavelet noise reduction, but no deconvolution.
Aspen CG16M, PlaneWave 20" CDK. Field 36'arc, north up.
Thanks so much Peter. I think we're starting to see that the strength of the 20" under fairly ordinary Central Western NSW seeing (altitude 666m) mostly round 2 to 2.5 sec arc is faint stuff, not sharp stuff, and that binning and long subs are our friends.
Are you going to add colour? Might have to wait several years.
Cheers! We have 9x30 2x2 + 8x30 unbinned OIII, but I think we'll just have to start again with longer deeper subs. Sadly, the guide camera A/D offset is playing up and summer is a-coming in.
wow- that is great - so much going on in the faint stuff!
would be interested to see the difference you had with the 10 hrs of 30 min 2x2 for comparison.
