Barnard’s E Dark Nebula
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February 4, 2015
I’ve sent around pictures of various types of nebulae: planetary nebulae like the Ring Nebula; red emission nebulae; blue reflection nebulae. But I’ve only photographed one dark nebula before (the Horsehead Nebula). The Barnard catalogue contains a collection of dark nebulae — patches relatively devoid of stars due to soot and dust that block out the light of the stars behind them. They can create some really interesting patterns. The Horsehead Nebula is silhouetted against a red reflection nebula. But dark nebulae are often framed against the rich starry background of the Milky Way. That’s the case in the attached image, where B142 (upper right) and B143 (bottom left) combine to make the shape known as “Barnard’s E.” It is located about 2000 light years from us in the constellation of Aquila, the Eagle.
SBIG STL-11000M camera, Baader LRGB filters, 10″ f/6.8 ASA astrograph, MI-250 mount. Guided with STL-11000’s external guider and a 500mm f.l. Lumicon guide scope. Acquistion and guiding using Maxim-DL. Focused with FocusMax. Shot from my SkyShed in Guelph, Ontario. No moon, above average transparency and seeing.
11x10m L, 4x5m L (total of 115m L), and 7x2m for each of R,G and B (total of 2hr52m).
L, R, G and B masters were cropped and the colour channels wer combined to make an RGB image which was processed with DBE and ColourCalibration. HistogramTransformation was applied.
DBE was applied to neutralize the background. HistogramTramsformation was applied.
Combining L with RGB:
The luminance channel of the RGB was extracted, processed and then added back into the RGB image as follows:
1. Extract luminance from the RGB image.
2. Apply LinearFit using the Luminance as reference.
3. Use ChannelCombination in the Lab mode to replace the luminance of the RGB with the fitted luminance from step 2.
4. LRGBCombine was then used to make a LRGB image.
TGVDenoise was applied to the L only, followed by CurvesTransformation to darken the background. A copy of the image was made and LinearMultiscaleTransform was applied to extract the first 4 wavelet layers (no residual). This image was used as a mask to protect the background while ColourSaturation was applied to the star cores.
Image scale is about 1.1 arcsec per pixel for this camera / telescope combination.