NGC1579, The Northern Trifid Nebula

NGC1579

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March 29, 2015, Picture of the Day at Astronomy Magazine Online

Astronomy Magazine Online May 12 2015The Northern Trifid Nebula is smaller and further away than its namesake, lying 2,100 light years away in the constellation Perseus.  It is about 3 light years across and contains both reddish and blue components.  The blue is reflection nebula, where dust behind the stars reflects starlight.  The red in this case is not from the usual emission of hydrogen.  According to NASA’s APOD write-up, it is the light of a massive young star that emits strongly in hydrogen alpha, and whose light is being dimmed and reddened by dust within the core of the nebula. To either side of the nebula additional dust and soot is evident in large areas that contain few stars.

This image was acquired over 9 nights between January 20, 2015 and February 27, 2015.

Tekkies:
SBIG STL-11000M camera, Baader RGB filters, 10″ f/6.8 ASA astrograph, Paramount MX.  Guided with STL-11000’s external guider and 80 mm f/6 Stellar-Vue refractor.  Acquistion, guiding and calibration done using Maxim-DL.  Focusing with FocusMax.  Automation with CCDCommander.  Registration, integration and all processing in PixInsight.  Shot from my SkyShed in Guelph, Ontario.  moderate moonlight for RGB, no moon for L; gibbous to full moon for Ha.

18x10m R, 16x10m G, 16x10m B, 35x10m L and 22x20m Ha unbinned frames (total=21hr30m).

RGB:
Creation and cleanup: Ha, L, R, G and B masters were cropped.  R, G and B were combined to make an RGB image which was processed with DBE and ColourCalibration.  The Ha image was also processed with DBE and the NB-RGB Combine script was applied to blend the Ha into the RGB.

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 (50 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 20 stars).

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

Dynamic Range Adjustment and Stretching: HDRMultiscaleTransform was applied at 6 and 4 pixel scales, protecting bright stars with a mask. TGVDenoise was applied in RGB/K mode with default settings, followed by HistogramStretch.  A range mask was made that protected stars and background, and LocalHistogramEqualization was applied to the nebula.

Synthetic Luminance:
Creation and cleanup: The cropped L, 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). DBE was applied to neutralize the background.

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 (100 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 20 stars).

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

Dynamic Range Adjustment and Stretching: HDRMultiscaleTransform was applied at 6 and 4 pixel scales, protecting bright stars with a mask. TGVDenoise was applied in RGB/K mode with default settings, followed by HistogramStretch.  A range mask was made that protected stars and background, and LocalHistogramEqualization was applied to the nebula.

Combining SynthL with HaRGB:
The luminance channel of the HaRGB was extracted, processed and then added back into the RGB image as follows:
1. Extract luminance from the HaRGB image.
2. Apply LinearFit using the SynthL channel as a reference.
3. Use ChannelCombination in Lab mode to replace the HaRGB’s luminance with the fitted luminance from step 2.
4. LRGBCombine was then used to add SynthL to make a LHaRGB image.

Final Processing

Star Colour Adjustment: Luminance was extracted from the LHaRGB image and LinearMultiscaleTransform was applied to extract the first 4 wavelet layers (no residual).  This image was blurred using convolution (scale= 3 pixels) and was used as a mask for ColourSaturation to boost colour in the star cores.

Final Steps:  A contrast adjustment was applied and the background was darkened slightly.

Image scale is about 1.1 arcsec per pixel for this camera / telescope combination.

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By | 2015-05-12T06:54:46+00:00 March 29th, 2015|Nebulae|2 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.

2 Comments

  1. luciano commissari March 31, 2015 at 12:08 am - Reply

    Very beautiful the stars and the detail of the nebula. Congratulations Ron a nice job. Even the sky background is well calibrated.

  2. Mark April 1, 2015 at 5:10 pm - Reply

    Nice image, Ron.

    It’s uncanny how like ‘our’ Trifid it is – except of course for the beautiful blue! I suppose knocking down the wall of your observatory to get at it would be a bit extreme!!!

    As always, your processing notes are are great – each one a lesson in Pixinsight.

    Mark

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