Sh2-115 Emission Nebula (H-alpha)
July 21, 2015
Sh2-115 is in the right half of the image, with most of Sh2-116 towards the left. Both are members of the Sharpless catalogue of nebulae and lie in northern Cygnus, not far from the famous North America nebula. They lie about 7500 light years away. At the distance of this nebula, this image spans about 120 light years from top to bottom. The clouds of glowing gas are powered by the stars in the open cluster Berkely 90, which is slightly to the lower right of centre in this image. The stars’ energy is exciting hydrogen electrons which then release red light when they drop back to their normal energy state.
This image shows only the data collected through the deep red hydrogen-alpha filter. This object also looks beautiful in colour.
SBIG STL-11000M camera, Baader Ha filter, 10″ f/6.8 ASA astrograph, Paramount MX. Guided with STL-11000’s external guider and 80 mm f/6 Stellar-Vue refractor. Acquisition and guiding with TheSkyX. Focusing with FocusMax. Automation with CCDCommander. Calibration, cosmetic correction, registration, integration and all processing in PixInsight. Shot from my SkyShed in Guelph, Ontario. No Moon. Good to very good transparency and good to very good seeing throughout acquisition.
13x30m Ha unbinned frames (total=6hr30m).
Creation and cleanup: Ha master was cropped and processed with DBE.
Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the background areas. Layer settings for threshold and strength: Layer 1: 3.0, 0.5 Layer 2: 2.0, 0.35 Layer 3: 1.0, 0.2 Layer 4: 0.5, 0.1
Deconvolution: A copy of the image was stretched to use as a deconvolution mask. A star mask was made from unstretched SynthL to use as a local deringing support. Deconvolution was applied (100 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 20 stars; local deringing at 70% and global dark deringing at 0.02).
Stretching: HistogramTransformation was applied to make a pleasing yet bright image. TGV Noise was applied and the image was re-stretched to reset the black point.
Overall contrast was increased and brightness increased slightly with the Curves tool.
Image scale is about 1.1 arcsec per pixel for this camera / telescope combination