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Cygnus Loop, HOO

The Cygnus loop (radio source W78 or Sharpless 103) is a large expanding cloud of hot dust and gas born of the death explosion of a massive star in the constellation of Cygnus. The nebula is 1,500 light-years away and the supernova that created it occurred 5,000 to 8,000 years ago and would have been bright enough to be seen with the naked eye from Earth.

Processing Details

PixInsight

StarAllignment of the linear Hydrogen-α and Oxygen III data using the Hydrogen-α frame as a reference.

DynamicCrop on both of them using the same process.

Background Noise removal with AutomaticBackgroundExtractor on both frames.

LinearFit on the integrated Hydrogen-α frame to balance the emissions, as the emissions of the Oxygen III are weaker than the Hydrogen-α frame (the nebulosity is stronger in the Hydrogen-α frame).

Noise reduction with MultiscaleLinearTransform. 4 layers with the following settings (R as default):

  • Layer 1: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 2: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 3: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 4: Threshold 0.500, Amount 0.50, Iterations: 1

The PixelMath formula:

  • R: HA

  • G: HA * 0.2 + OIII * 0.8

  • B: OIII

Optimisations with CurvesTransformation and STF auto-stretch (linked RGB Channels) with the HistogramTransformation.

Further noise reduction using ACDNR with the following settings:

Lightness: (StdDev 1.0, Amount 0.20, Lightness mask enabled, Bright Sides Edge Protection - Threshold 0.015, Overdrive 0.00)

Chrominance: (StdDev 0.1, Amount 1.00, Lightness mask enabled, Bright Sides Edge Protection - Threshold 0.030, Overdrive 0.00)

Photoshop

Further colour and balance optimisations with Camera Raw Filter.

Tech Card

Date / Location

August - September 2019, Bedworth, GMT+0, United Kingdom, Bortle Class 5 ~SGM: 19.57 mag./arc sec2

Equipment

Camera: ZWO ASI 1600MM-PRO USB 3.0 Mono (Type CMOS)

Sensor Cooling Temperature: -15C

Filters: 1.25" 5nm Astrodon Ha, 1.25" 3nm Astrodon OIII

Imaging Telescope: Takahashi FS-60CB

Correcting Lens: Takahashi Reducer 0.72x (composite focal length at 264mm and focal ratio at f/4.9)

Mount: iOptron CEM25EC

Image Quality

12Bit ADC (FITS)

Exposure time per image / number of composities and sensitivity

32 x 180" Ha subs (Gain 139, Offset 21, Binning 1x1)

28 x 300" Ha subs (Gain 139, Offset 21, Binning 1x1)

13 x 600" Ha subs (Gain 139, Offset 21, Binning 1x1)

24 x 180" OIII subs (Gain 139, Offset 21, Binning 1x1)

28 x 300" OIII subs (Gain 139, Offset 21, Binning 1x1)

12 x 600" OIII subs (Gain 139, Offset 21, Binning 1x1)

Total Integration Time

11hrs 38mins

Calibration Frames

20 Darks, 20/20 Flats for Ha/OIII

Software

PixInsight 1.8 Core

Photoshop

SharpCap