IC1396 large OOH NB mosaic

[timh]

Williams Zenithstar 110 mm F 7.0 apochromat (TMB -designed lens) - reduced to F5.5 using a WO III reducer flattener, Moonlite focuser and focus controller, Ioptron CEM70G mount, 80 mm f = 400 mm guide scope with ZWO ASI 120MM camera, ZWO AI294 MM main camera. Antlia 3 nM OIII filter or Optolong 7 nM HA filter. Optical train locked using a Baader clicklock.

11 x images in HA and in OIII taken over several nights where each image comprised ~ 1.5h of data (should have been 9 images - alignment inefficiencies) captured - along with flats and darks - in Sharpcap. Pre-processing in PixInsight. Each panel was processed in PixInsight firstly using Multiscale Gradient (MARS data) subtraction, slightly sharpened (there is little effect at 1.545 arcsec/ pixel) using Blur Exterminator, co-aligned using Astrometry and the Mosaic script, co-calibrated using the DNAlinear script and then combined into mosaics using the mosaic process with Averaging applied over the overlaps. The HA and OIII mosaic images were then co-aligned and co-clipped. Each mosaic was then once again background-subtracted using the MARS multiscale background removal process. The two sets of stars were then removed and retained as star images using RC Star Exterminator. The two starless images were stretched using the multiscale stretch tool. The OIII image being weaker was slightly boosted using Arcsinh and the noisier outer dark regions where there was effectively zero signal improved by cloning over from one of the better ~ zero signal - signal to noise dark panels. The starless images were then combined into a single narrowband HOO image using Pixmath with some part (10% and 15%) of HA signal included in the G and B channels (to account for H beta). The starless image was then stretched up using the EXP and Arcsinh processes and colour hue adjusted using Affinity Photo. The two star images were similar similarly recombined and - at a suitable stretch - readded back into the starless image. Finally RC Noise Exterminator at 0.3 and default parameters was applied to minimise luminance and colour noise.

The 'garnet star' is obvious - and somewhat bloated - at bottom left and IC1396a - the eroding molecular cloud dark nebula the "elephant's trunk" near the centre along with HD206267 the massive young triple star ionising the entire huge molecular and gas cloud which is about 2500 ly distant. As expected --corresponding to the highest electron temperature region the fainter blue O3 signal is mainly located nearer the centre of the nebula.

A bit of a Sisyphusian task with my current set up. The PI tools worked well to provide a consistent background and the foreground dark nebulae are quite striking even towards the edges of the image. But took a long time so maybe this sort of task is better attempted at a shorter focal length and losing some detail?

I have provided a link to Flickr for the full depth image that I hope works OK

https://www.flickr.com/photos/204508644 ... ed-public/