Sh2-112
Sh2-112 - Click here for full resolution
SH2-112, also known as LBN 337, is a diffuse emission nebula located about 5,600 light-years away in the constellation of Cygnus. This is a circular region of HII with dark dust rifts that can be seen on the western side. The star responsible for its excitation is believed to be BD+45 3216, a double blue star of spectral class O8V with an apparent magnitude of 9.18. It is located in a portion of the Orion Spiral Arm that is noted for areas of rich star formation.
source: cosgrovescosmos
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LBN337
Emission Nebula
Cygnus
20h 33m 49s
+45° 38.0′
01 Sep
82º N
Conditions
Sh2-112 is a better target for early autumn, with peak altitudes of 82° in early September. But also in May-June it reached decent altitudes towards the second half of the night from the remote observatory at IC Astronomy in Oria, Spain. As such it was a good target to image during the full moon period at the end of May. Conditions were not great each night, and images were taken over 13 nights between mid May and mid June 2024.
Equipment
The default rig at the observatory was used. This is built around a Planewave CDK-14 telescope on a 10Micron GM2000 mount, coupled to a Moravian C3-61000 Pro full-frame camera. The RoboTarget module in Voyager Advanced automated the process to find optimal time-slots during astronomical night.
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14, Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro, cooled to -10 ºC
Chroma 2” H-alpha, SII and OIII (all 3nm) unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Windows 11, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.8.9-3
Imaging
Many Sharpless objects are relatively large regions of HII gas. Sh2-112 is relatively small with a diameter of around 25 arcmin. But it is fairly bright and shows lots of detail. It can be imaged very well in Ha-RGB, but it also has a pretty bright OIII region in the middle, so in this case the choice was made to image using all three narrowband wavelengths and process in the HSO Hubble palette. No separate RGB images for stars were taken. Images were shot using exposures of 10 min each and a total of 24h of data was acquired.
Resolution (original)
Focal length
Pixel size
Resolution
Field of View (original)
Image center
6785 ×4905 px (33.3 MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
48' x 32'
RA: 20h 34m 01.617s
Dec: +45° 38’ 57.72”
Processing
All images were calibrated using Darks (50), Flats (25) and Flat-Darks, registered and integrated using the FastBatchPreProcessing (FBPP) script in PixInsight. This is a new script in the recently released version 1.8.9-3. This script is fully focused calibration at maximum speed. It comes at the cost of less fine-tuning options for challenging situations. But if you have a decent good data set with several tens or hundreds of images, not too much changing gradients and not much distortions in the image, FBPP will give you 99% of the quality at a fraction of the time. The current dataset consisted of 144 light frames and 175 calibration frames, and took 9m 41s to fully calibrate and stack. While not having a direct comparison at hand using WBPP (which can also be tuned to ‘faster’ or ‘better’) on this dataset, typical experience would be that it would more likely take two or three hours to process. This is a major improvement in the processing workflow, which I plan to use from now on as the new default.
Gradients were removed per channel using GraXpert, then combined into the Hubble palette (SHO). SPCC was run in ‘narrowband mode’ with ‘Photon Flux’ as White Reference. BXT was able to really sharpen up the nebulous details pretty well. Stars were removed and discarded. Stretching was done using the Unlinked Stretch script from Bill Blanshan. I did not want to push the stretching too far, as the most important step was the next one, to define the Hubble Palette. This was done using the NarrobandNormalizaiton. The SHO palette was chosen with Ha for Lightness. SCNR was increased quite a bit and also OIII and SII were given a decent boost. The result was a pretty decent Hubble Palette, but with a bit of a magenta cast in the background. This was removed by inverting the image, run SCNR and inverting it back again. After some contrast enhancement, the saturation of the blues was further enhanced using CurvesTransformation and a blue mask generated using the ColorMask script. After removing the noise with NXT, the starless SHO image was pretty much ready
There were no separate R, G and B images recorded for star colour, so the proper colours should be obtained from the narrowband images. SetiAstro has created a script for this specific situation. To get the individual narrowband images ready for this, they were sharpened with BXT before stars were extracted. Then each channel was loaded in the tool, and stretch setting (5) was also selected. I felt that the colours that came out were too intense to my taste, so the color boost slider was reduced to something like 0.6. The result of this tool is actually a pretty good looking set of RGB stars.
Stars and SHO image were combined using the ImageBlend script. A tiny bit of green cast in the center portion of the image was removed with SCNR at 0.2. Then the image was cropped in to get a better composition of the nebula. Blues were enhanced yet again a tiny bit by pulling down the CIE b* component at around the 0.35 mark. This completed the processing to the final image.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
