The Great Rift in the Soul Nebula (SH2-199, contains IC 1871) in Cassiopeia

Gold Canyon, AZ
October 30 – November 4, 2021

The Great Rift in the Soul Nebula was the second target of three imaged each night in Arizona.  Hydrogen-a, Oxygen-III and Sulfur-II 7nm narrowband filter data were combined using the Hubble pallet by assigning S-II to the red, H (with about 20% O-III) to the green, and O-III to the blue channel (SHO).  I used an evaluation copy of Russ Croman’s StarXTerminator tool in PixInsight to remove the stars so that the nebula could be processed separately from the star field.  StarXTerminator worked exceedingly well on all three linear monochrome images.  The stars image from the H integrated data was used to create a RGB star field.  The Ha star field had smaller and fewer stars, and all stars were white as only one monochrome image was used.  Starless and stars images were processed separately in PixInsight.  It turns out that the processing of starless images was much easier and faster than with conventional images.  A luminance image was extracted from the combined SHO color image.  The luminance was denoised, stretched and sharpened, while the RGB image was denoised, stretched and blurred.  The luminance was combined with the starless RGB image, and the saturation and color balance was adjusted.  The starless and stars images were combined using the PixelMath combine function with op_screen() to produce the final color image.

The Great Rift, IC 1871, is part of the much larger Soul Nebula (SH2-199, IC 1848) in the constellation Cassiopeia.  It contains the rift and both emission and dark nebulae.  While the Heart and Soul nebulae are popular objects for widefield imaging, there are some very interesting formations for telescopes with long focal length, the Great Rift being one.  IC 1871 is about 6,500 light years from Earth (Astronomy, October 2018).

Imaging details:

Celestron 9.25" Edge HD SCT
Celestron 0.7x Focal Reducer (FL = 1645mm, f/7)
Celestron off-axis guider with a ZWO ASI 174MM mini guide camera
Losmandy G11 mount with Gemini 2
ZWO ASI 2600MM Pro cooled monochrome camera (-10oC)
ZWO 36mm Hydrogen-, Oxygen-III and Sulfur-II filtersRA: 44.3235o, DEC: 60.6593o, Equatorial camera rotation: 340o
Software:    Sequence Generator Pro, ASTAP plate solving, PHD2 guiding, 
    Losmandy Gemini ASCOM mount control and web client interface,
    SharpCap Pro for polar alignment with the Polemaster camera,
    PixInsight 1.8.8-10 with StarXTerminator,
    Photoshop CC 2022

Hydrogen-alpha    10 min x 47 subframes (470 min), Gain 100, Offset 68, 1x1 binning
Oxygen-III    10 min x 37 subframes (370 min), Gain 100, Offset 68, 1x1 binning
Sulfur-II    10 min x 45 subframes (450 min), Gain 100, Offset 68, 1x1 binning