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Thor's Helmet ( NGC 2359 ) in the constellation Canis Major
Thor’s Helmet ( Duck Nebula, NGC 2359 ) ( please click / tap on image to see larger )
This HDR image shows the bright nebula Thor’s Helmet in a sea of colourful stars against a background of red from dust and HA emissions. The stars in this image range from the brightest ( bottom right, HD 56501 ) at magnitude +7.7 to around +20 or more. HDR capture and processing allows all of the stars to be portrayed in colour without any burnt-out highlights. The colours of the stars and nebula are as close as I can get them to their "true colours" by using a "daylight colour balance" and allowing for the extinction of blue-green due to atmospheric absorption/scattering ( mean altitude during capture ~ 60deg ).
The blue star in the centre of the bubble of expanding stellar material is HD 56925 ( WR7 ) - a massive, unstable and short-lived Wolf-Rayet star that one day will detonate in a supernova.
NGC 2359 Thor’s Helmet / Duck Nebula: Magnitude +11.5, RA (2000.0) 7h 15m 37s, Dec -13deg 12' 8", approx. 1800 light years away
HD 56925 / Wolf-Rayet 7 ( WR7 )
Resolution ........ 1.318 arcsec/px
Rotation .......... 0.00 deg ( North is up )
Focal ............. 1398.41 mm
Field of view ..... 57' 40.8" x 38' 29.0"
Image center ...... RA: 07 18 36.509 Dec: -13 11 53.38
Telescope: Orion Optics CT12 Newtonian ( mirror 300mm, fl 1200mm, f4 ).
Corrector: ASA 2" Coma Corrector Quattro 1.175x.
Effective Focal Length / Aperture : 1410mm f4.7
Mount: Skywatcher EQ8
Guiding: TSOAG9 Off-Axis-Guider, Starlight Xpress Lodestar X2, PHD2
Nikon D5300 (unmodified) (sensor 23.5 x 15.6mm, 6016x4016 3.9um pixels)
Blue Mountains, Australia
Moderate light pollution ( pale green zone on darksitefinder.com map )
Capture ( 18 & 19 Jan 2018 )
9 sets of sub-images with exposure duration for each set doubling ( 1s to 240s ) all at ISO 250.
116 x 240s + 5 each @ 1s to 120s
Processing ( Pixinsight - 20 Jan 18 )
Calibration: master bias, master dark and master flat
Integration in 9 sets
I'm starting a new thread for this since the hydrogen data is rather old and it has been reprocessed since I posted a while ago.
Now I finished the acquisition of O[III] too. Or sort of, I planned more, but clear nights were so rare that I decided to process what I had.
The image was done in "3 pass" data over the area. That means that I acquired 3 sets of images covering the same area and combined in the end. First 2 in hydrogen, the last in oxygen.
First set consisted of 3 panels in portrait mode for the top area and then I wanted to extend them to the bottom so I shot another 2 panels in landscape mode.
I knew that I could get a higher SNR so I shot 4 more panels in landscape mode.
Each panel consists of 30-31 subs, each sub 300s.
Then I started the acquisition of O[III] which needed light pollution and moonlight conditions than the Ha required.
Top panels contain 30 subs, but the bottom ones, only 20-22. Each 300s. Luckily there's not much oxygen in that area so I could get away with less subs.
I also took some 10s-30s frames for M42's core.
For the framing, I created a quick mosaic of the same area.
For the final alignment I shot an image somewhere close to the center of this area. I can't remember if the initial register was done in APP or Registar - for the first pass, but for the next ones it was done in Registar.
I removed the gradient manually in each stack with APP and then I created the mosaics for each pass same with APP.
The 2 Ha passes I then blended manually 50%-50%.
For the processing, I tried to stretch both Ha and O[III] to the same levels and I combined them manually in some 60-40/70-30 ratio for a layer which I used as lum.
The colours were Ha - reddish, O[III] - cyan-blue.
I spent a lot of time trying to control the big stars, the O[III] filter has poor coatings and, together with the ASI1600s non AR coated sensor, I had much brighter reflections than with the Ha filter.
And I tried to raise the oxygen levels selectively around the flame and NGC2023, but the flame is really dim in O[III].
Don't know what other details in the story I forgot, this project drained me a lot of energy.
Camera was ASI1600MMC, cooled to -15C for the first pass and to -25C for the ones following. Gain 139.
Canon 300 F4 L IS lens with a lot of aberrations towards the edges.
AZ-EQ5 mount guided with a 200mm lens and an ASI120MM, with varying seeing. 1.5-2.5" RMS guiding error usually.
APT for capture, PHD2 for guiding, Registar for each night initial alignment.
DSS, APP, Registar, StarTools, GIMP for processing.
I started shooting early in October and I wanted much more, but Orion already becomes less and less visible from where I image and hides beyond the house. Ah, yes, I image from a yellow-pink light polluted area.
Thanks for reading, thanks for looking! Comments and suggestions are appreciated.
Links to original image and acquisition details: