Seagull Nebula

Seagull NebulaClick image for full size version

February 20, 2017

The Seagull Nebula includes several objects.  The “head” is IC2177, also known as Gum 1, VDB 93, and Sh2-292. The image also contains two open clusters (NGC2335 and NGC2343) towards the left of the image and there is much surrounding dust. The bright patch at right is Sh2-297. I created an annotated image to show where these objects are located, as well as a number of PGC galaxies. The complex lies about 3,650 light years from earth in the constellation Monoceros. This is my first new image in month; I have been clouded out since mid-December. I processed it during the 2017 Winter Star Party, where I am scheduled to deliver a lecture tomorrow and a workshop the day after. 

Tekkies:

Moravian G3-16200 EC camera (on loan from O’Telescope), Optolong Ha, R, G and B filters, Takahashi FSQ-106 ED IV at f/3.6, Paramount MX, QHY5 guide camera, 175mm f.l. guide scope. Acquisition with the SkyX, focused with FocusMax. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Gibbous moon for Ha, no moon for RGB, average transparency and seeing.

12x10m R, G and B; 8x20m Ha unbinned frames (total=8hr40m). 

NB-RGB Creation
Creation and cleanup:  R, G, B and Ha masters were cropped and processed separately with DBE. R, G and B were combined to make an RGB image which was processed with ColorCalibration. The NBRGBCombination script was run with default settings using Ha for red narrowband. 

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

Stretching:  HistogramTransformation was applied to make a bright, pleasing image. 

Synthetic Luminance:
Creation and cleanup of SynthL: The cleaned up Ha, R, G and B masters were combined using the ImageIntegration tool (average, additive with scaling, noise evaluation, iterative K-sigma / biweight midvariance, no pixel rejection).

Deconvolution:  A star mask was made to use as a local deringing support. A copy of the image was stretched to use as a range mask. Deconvolution was applied (80 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with 18 stars).

Linear Noise Reduction:  MultiscaleLinearTransform was used to reduce noise. Layer settings for threshold and strength: Layer 1: 3.0, 0.6   Layer 2: 2.0, 0.45  Layer 3: 1.5, 0.33  Layer 4: 1.0, 0.2 and Layer 5: 0.5, 0.13.

Stretching:  HistogramTransformation was applied to make a bright, pleasing image. 

Noise Reduction and Re-Stretch: TGVDenoise was applied in Lab mode with 300 iterations with a range mask used to protect high signal areas.  This was followed by a HistogramTransformation to raise the black point (but with no clipping). 

Combining SynthL with NB-RGB:
The processed SynthL was applied to the NB-RGB image using ChannelCombination in Lab mode with default settings.

Additional Processing

Contrast Enhancement: LocalHistogramEqualization was applied to the brightest parts of the nebula at two different scales (scale 50, strength 0.5, max contrast 2; scale 150, strength 0.2, max contrast 1.5).

Noise Reduction and Re-Stretch: TGVDenoise was applied in Lab mode with 300 iterations with a range mask used to protect high signal areas.  This was followed by a HistogramTransformation to raise the black point (but with no clipping). 

Final Steps: MultiscaleLinearTransform was used to sharpen the brightest parts of the image, using a mask to protect other areas (Layers 2-4 settings:  0.10, 0.10, 0.06). Background and star brightness, contrast and saturation were adjusted in several iterations using Curves with masks as required.  

Image scale is 3.2 arcsec per pixel for this camera / telescope combination.

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By | 2017-02-21T08:26:17+00:00 February 20th, 2017|Nebulae, Open Clusters|0 Comments

About the Author:

An avid astrophotographer who has been hunting deep sky treasures with his camera and telescope for many years now. He enjoys sharing the amazing cosmos with others.

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