Resolving the core of the catseye. Lucky imaging maybe?

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timh
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Joined: Mon Aug 26, 2019 5:50 pm

Resolving the core of the catseye. Lucky imaging maybe?

Post by timh »

The core of the catseye nebula NGC6543 in Draco is compact - 16-20 arcsec - and quite bright (Mag 8.2) and so seemed planet-like enough that it might just be susceptible to lucky imaging techniques? Here I had a go and had some success but concluded that getting it to work convincingly would probably require something bigger --maybe a 16 inch Dob at F 4 or so?

200 mm PDS SW Newtonian plus Baader flattener at F 5.0 on an Ioptron CEM70 mount. Bortle 6. Moon full and one day before full

ASI 294 MC camera at -10C - oixel size 4.63 uM
ASI 294 MM camera at - 10C at BIN 1. - pixel size 2.315 uM

Expt 1. Was to use conventional deepsky imaging. 93 x 10s ASI 294MC exposures at gain 124 (near unity) were selected in SC and analyzed in PIxInsight indicating an average FWHM resolution score of < than 2.5 arc sec (i.e all the frames were sharp). Preprocessed , stacked and processed in Pixinsight - using a high dynamic range transformation to bring out detail in the bright core yielded image A. The image scale here is 0.95 arcsec/ pixel.

Expt 2. was a 320 x 240 pixel SC capture of an 8 bit RGB AVI file at maximum gain 570 and 2396 frames of exposure length 100 ms using the ASI294 MC. These were debayered in PIPP and 270 frames selected, stacked and processed in Registax to produce image B (same image scale as above).

Expt 3. was a 320 x 240 SC capture of an 8 bit mono AVI file at maximum gain 570 using the ASI 294MM. From an initial 17000 frames only a hundred or so were stacked to produce image C. The image quality was very poor using the BIN1 smaller pixels (image scale 0.425 arcsec/ pixel)

The conventionally obtained image A was not at all bad - the best that I have had of the catseye core anyway. In principle though, lucky imaging at exposures < 100 ms should be able to resolve better than the seeing limit of 2.5 arc sec.

However, even with a sensitive MONO camera at maximum gain this object appeared simply not to be bright enough (or uniformly bright enough) to capture adequately exposed frames at 100ms for the method to work at a pixel size and image scale (0.425) that could, in principle have improved resolution down to about an arcsec (Image C.)

Neverheless lucky imaging did work - and reasonably well in image B at an image scale of about 1 arc sec/ pixel - but then providing only marginally if any improvement in resolution over conventional imaging -- and with a total imaging time of only 27s - at a cost of decreased detection of light.

Possibly a quixotic quest but it seems to me that in principle this approach could still work for the catseye but that it would just take maybe 4 x more light per pixel and a larger image scale - maybe a 16 inch dob or a C11 might be up to the task if any one maybe has already tried it?

TimH
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oopfan
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Re: Resolving the core of the catseye. Lucky imaging maybe?

Post by oopfan »

Hi Tim,

A very interesting experiment! I like the detail of the inner core in image B, but I am at a loss to explain why the central star is so large. It makes me believe that it was dancing around from frame to frame. What does a typical single frame look like? I am surprised that Registax couldn't tame it. But then again this is not a typical lunar landscape.

Brian
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Menno555
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Re: Resolving the core of the catseye. Lucky imaging maybe?

Post by Menno555 »

Tim

I did some testing. Meade LX200 8" f/10 ACF with a Zwo ASI071MC Pro.
Just a quick and dirty test. I did try 100ms but that became too noisy. Maybe also the full moon is not helping now :)
On the left captured in full resolution of 4944 x 3284 and on the right with a ROI of 1920 x 1080.
Full resolution was saved as FITS and stacked in DeepSkyStacker and the ROI I saved as SER, debayerd in PIPP and stacked in PlanetarySystemStacker (this gave a much sharper image then AstroStakkert did)
Cropped and doubled the image size.
Both with the same settings: 600 x 250ms / Gain 400 / Brightness 10

Menno
Lucky_Cat.jpg
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timh
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Joined: Mon Aug 26, 2019 5:50 pm

Re: Resolving the core of the catseye. Lucky imaging maybe?

Post by timh »

Thanks folks,

It is certainly fun comparing different methodologies and also improves my understanding of quite where the limits lie

Brian, yes indeed the image was never stable and the problem I had in stacking that there was not a single image that could act as a good reference - and provide a decent basis for alignment points ---hence that bloated core.

Menno, yes maybe one area to experiment in would be to go longer than 100ms? The problem is that the proportion of 'good seeing' frames will drop and so the number of frames will have to increase?

I am not sure whether or not there is a higher surface brightness planetary core than the catseye to try out on?

I think what probably will work with the equipment I have available - and probably better for your set up Menno? - - is at the core of one or other of the globular clusters- say M13? Plenty of light - some structure to resolve - might be interesting to try down at 50ms or so?

TimH
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