Crescent and Soap Bubble Nebula - HOO

[Richard_]

This is a first "quick look" at my current data on NGC 6888 Crescent Nebula. I didn't realise at first, but I also captured the Soap Bubble Nebula (PN G75.5+1.7) at the bottom edge of the image. This is quite faint and has proven a challenge to bring out without affecting the nebulosity inside the bubble. I didn't bother with all the fancy pre-processing techniques, I just used PixInsight's WBPP script and used those master lights. I'll do all the fancy techniques once I have more data.

Image acquisition details and processing can be found below the image. Comments and criticism are welcome!

Full Image on Astrobin: https://www.astrobin.com/4iww8k/

From NASA:

"NGC 6888, also known as the Crescent Nebula, is a about 25 light-years across blown by winds from its central, bright, massive star. The oxygen atoms produce the blue-green hue that seems to enshroud the detailed folds and filaments. Visible within the nebula, NGC 6888's central star is classified as a Wolf-Rayet star (WR 136). The star is shedding its outer envelope in a strong stellar wind, ejecting the equivalent of the Sun's mass every 10,000 years. The nebula's complex structures are likely the result of this strong wind interacting with material ejected in an earlier phase. Burning fuel at a prodigious rate and near the end of its stellar life this star should ultimately go out with a bang in a spectacular supernova explosion. Found in the nebula rich constellation Cygnus, NGC 6888 is about 5,000 light-years away."

From Constellation-Guide:

"The Soap Bubble Nebula is a planetary nebula located near the larger and better known Crescent Nebula (NGC 6888) in the constellation Cygnus. Notable for its spherical symmetry, the faint nebula looks like a transparent soap bubble set against the rich stars fields of the Northern Cross region. It is catalogued as PN G75.5+1.7.

"It is a very faint object occupying only 4′ 20” of apparent sky and it is embedded in a diffuse nebula, which is why it was not discovered until recently. The nebula’s estimated distance is 4,000 to 5,000 light years."

"The Soap Bubble Nebula is not to be confused with the Bubble Nebula (NGC 7635), the famous emission nebula located in the constellation Cassiopeia, or with the other Bubble Nebula (NGC 6822), an emission nebula in Barnard’s Galaxy."

 

 

Acquisition Details

Camera: QHY268M (Readout Mode #1, Gain 56, Offset 25)

Telescope: WO FLT120 (with x0.8 reducer @ 624mm FL)

Mount: EQ6-R

Filters: Antlia EDGE 4.5nm (HO)

Filterwheel: QHYCFW3-M-US

Focuser: Pegasus Focus Cube 2

Guidescope/camera: WO 50mm / ASI290MM

• H: 31 x 300s = 2h35m
• O: 57 x 300s = 4h45m
• Total = 7hr20m

Location: South Wales, UK (Bortle 5 in my garden 🙂 )

Imaging Dates: 16-Sep-2022  |  17-Sep-2022  |  18-Sep-2022 

 

Darks: 30

Flats: 10

Bias: 100

Temperature: -5C

 

Processing Details

Calibration & Stacking

• All done in PixInsight
• Chuck all subs from multiple nights into WBPP script to calibrate and create master light for each channel

Master Lights

• StarAlign OIII to H
• H and O:
  • Crop to 6,150 x 4,050 pixels (remove stacking artifacts)
  • Deconvolution
  • NoiseXterminator
• Auto-STF each channel
• PixelMath combination with ForaxX HOO formula:

// R:
H

// G:
((OIII*H)^~(OIII*H))*H+~((OIII*H)^~(OIII*H))*OIII

// B:
OIII

• <<Remove stars with Starnet2>>
• SCNR (Green, 0.50)
• Curves
  • Gentle S-curve on RGB
  • Boost in red channel
  • Small boost in saturation
• Histogram Transformation
  • Slight stretch to red channel
• ColorMask
  • Script > ColorMask (create blue mask to protect OIII shell)
  • Convolution to soften mask
  • Apply mask and invert to protect OIII shell
• Curves
  • Red channel: keep darks fixed, slight boost to highlights
  • Blue channel: slight reduction in blue to reduce background cast
  • Slight hue shift: yellow -> red
  • Slight boost to saturation
• <<Re-insert stars with PixelMath>>
• Star Correction
  • Apply star mask
  • Script > Correct Magenta Stars
  • Remove star maks
  • Script > EZ Star Reduction (Adam Block method)
• Create mask for unsharp mask
  • Extract luminance layer
  • MultiScaleLinear transformation to soften layer 2
  • Apply mask to image
• Perform unsharp mask
• Save image 🙂