I am perhaps being a little impatient in imaging The Flaming Star and Tadpoles Nebula at this time of year, it would really be better placed in a months time. At the moment Auriga rises for me around 11:30pm so most of the imaging is for 4-5 hours post midnight. With my focal length of 360mm and image sensor the field of view allows excellent placement of both objects. The Flaming Star Nebula has designation IC405 and Tad Poles Nebula IC410, the two objects are not connected. I took this image on the night of 3rd Nov 2022. Unfortunately I was contending with a half moon and some high hazy cloud which caused some issues with quality and therefore the metrics I use to filter out 'good' from the 'bad' images', I'll get on to the impact which led to revisiting those metrics and an experiment akin to my Elephant Trunk run I did in November 2021.
Within Auriga (the Charioteer) the white rectangle.
Two fabulous objects for one. as can be seen below. IC405, tThe Flaming Star Nebula is around 1,500 light years away and about 5 light years across. It is lit up by the star AE Auriga, which was not actually born in this nebulosity, it is what is known as a runaway star that happens to be rushing through this area of gas, wikipedia mentions that this causes a bow shock which I interpret as the ripple effect.
Catalogue number NGC 1893 actually refers to the open cluster of stars embedded within the Tadpole Nebula which has its own catalogue number of IC410. The star cluster and nebula are around 10 times further away from us than the Flaming Star at 12-15,000 light years, at about 4 million years old these 'tadpoles' are fresh in cosmic terms! Tadpoles are of course Dust and Hydrogen gas and probably are active areas of star formation. They are actually approximately 10 light years long.
Capture
2022-11-03
Exposure at ISO800, 240s using the Optolong L-Enhance Filter
Lights - 86
Darks - 30
Flats - 30
The Darks here where made up of 10 taken just before starting imaging at 7.9ºC and 20 at finish of processing at 4.5ºC. Dark calibration all about trying to take account of the thermal current on the sensor I made the decision to include both. My intention here is to start build up a library of Darks at given temperatures, I did this on this occasion during the evening while waiting for the target to get sufficiently over my horizon.
Pre-Processing
After registration of all sessions data total of 86 * 4m = 5h44m.
Removed:-
f = 3.5
r=0.8
w=5
48 images remaining, high cloud with the half moon in combination I put down as the reason for the drop in quality, many were rejected based on FWHM being above the 3.5 threshold, lets call this version 1. I also produced a version 2 where I increased the FWHM threshold to 4 to allow more (but lower quality images).
V1 - Stacked 48 * 4m -Total Integration Time = 3h12m
V2 - Stacked 68 * 4m -Total Integration Time = 4h32m
After going through the Post processing of both I was much happier with the look of V2. This lines up with my previous experience of the Elephant Trunk where the adage more is better (even if more brings in some images with lower quality) held true. My thoughts here are that with my fairly limited focal length I have quite a bit of leeway with quality before it affects a final image. I'm pretty sure if I was running at longer focal lengths I would need to be more circumspect with the filtering of bad images and V1 may well be the way to go.
Post Processing (V2 stacked images)
Siril
Crop - fairly minor to remove one corner of elongated stars and snip off the stacking artefacts
Rotate 180 - I like my flames rising!
Background Gradient - made a big difference using the RBF method, this is probably Moon related.
Colour Calibration Photometry
Deconvolution, Kernal size of 1.0
Asinh Stretch - 3 iterations with stretches of (30,30,8)
Histogram Stretch
Green Noise Removal
Starless and Stars created using Siril Pixel Maths and Starnet++.
Once we have a TIFF (16 bit version) of Starless move into PS.
Photoshop (PS) Processing
Levels & Curves - Careful here not to overly balance the channels, doing this initially resulted in a rather bland yellow fire not the raging red this nebula is known for.
Raw - Highlights and Contrast
Raw - Texture
Raw - Clarity
Raw - Colour Contrast
Raw - Noise Reduction
Raw - Saturation and Vibrancy and Shadow
Create FIT version of TIFF file output from PS using Siril
Once back from PS then Pixel Math Add the Stars back into the FIT version of the PS processed TIFF file using the formulae (starless+(0.8*stars)).
Created JPG version.
Final Thoughts
Two main learning points I took away on this image:-
There will obviously be limits but at the moment I can afford to lower the quality bar in the interests of getting more data, compared to this the V1 image was much noisier and lacked some depth. FWHM filter of 4 could be tried if struggling with integration time.
During Post Processing it is very easy to fall into a trap with Levels and Curves of balancing the histogram, i.e. making the RGB channels histogram curves look very similar. It is important to have a vision for the final output rather than blindly following a prescribed path which could leave all your images looking identical.
Anyway onwards and upwards. More data on this subject, perhaps one more night may be something I plan in the near future as Auriga rises earlier as we move through Autumn into Winter.