NGC7822. One night, 3 poor images but a good result

[timh]

Recently there was a single night's clear sky break in the weather but close to the full moon.

Being fortunate to have two imaging set ups - a 4/1 inch apo refractor and an 8 inch Newt along with the colour MC and mono MM versions of the ASI 294 Pro camera I thought that I'd go for it and run both set ups simultaneously to try and get enough data within a single night to produce a 'finished' NB image.

The refractor and Newt set ups were basically as described in my last few posts.

The PDS200-- Newtonian imaged at f=909mm (F 4.5) 1.05 arcsec / pixel using the MM camera and alternatively an Optolong 7nm HA filter or Antlia 3 nm OIII filter plus ZWO UV/ IR cut filter.

The 110 mm WO refractor images at f = 620mm (F5.6) 1.53 arcsec/ pixel using the MC camera and the Astronomik UHC filter plus Baader UV/IR filter.

The raw (drizzlex1) integrated images were about about 3h of HA, 3 h of OIII and about 4.5h of UHC-filtered RGB at the lower resolution. As shown below - none of the images were that great --the sky was bright because of the moon and there was some turbulence meaning FWHM values were high and stars occasionally mis-shapen. The HA data had all the interesting detail and completely overlapped the O3 data which was 15X or so weaker and noisier. So the only informative luminance was HA. Nevertheless the O3 image star shapes were good. The RGB data had good colour data but poor resolution and- being broadband - overexposed and bloated bright stars.

It was possible in the end though - through the miracle of PixInsight processing and RC star extraction and correction - to derive a reasonable NB image of NGC7822 with correctly-coloured and 'Newtonian -shaped' stars. The strategy was to 1) align all of the images to the same image scale 2
) use Blur Xt to correct star shapes and sharpen non-stellar slightly 3) transfer the O3 luminance to the RGB image and then extract out the now correctly shaped and coloured stars 4) derive the highest possible SNR Red, Blue and Green channels by combining the UHC and NB data as described in my last posting on the Elephants trunk image, 5) transfer in the luminance detail from the HA + R red channel , 6) combine/ process the starless image using Pixmath , Exp, Arcsin, Curves etc and 7) finally screen back in the RGB stars.

Images are shown below for interest ..

NGC7822 is quite a faint HII emission nebula in Cepheus . The image here shows only a very small part of it. The OIII is relatively faint -- I have seen some images amplifying this signal up to make some regions blue (with a concomitant increase in noise without a lot of OIII data) but I think I prefer it as shown as being more 'realistic'. The nebula and star-cluster region does have the distinction of comprising the hottest- 45000 K- type O star in the Orion arm of the galaxy known cf https://astroblog.cosmobc.com/ngc-7822/ and https://cosgrovescosmos.com/projects/ngc7822.