Image Acquisition

Broadband (RGB) data collected using UV-IR Cut filter on July 27 during “average”seeing and transparency conditions.  Narrowband (Ha and Oiii) data collected on August 1 using Optolong L-Extreme dual narrowband filter under “below average” transparency conditions.  Mean Sky Quality Meter reading was 20.70 magnitudes per square arcsecond (Bortle 4).  Waxing gibbous moon phase averaged 79.4% illumination over the two nights.

Guiding using ASI174MM camera in Celestron Off-Axis Guider.   Drift in the right ascension axis averaged -3.09 arc-sec/min or -3.63 px/min; drift in declination axis averaged +0.18”/min or +0.21 px/min.  Pixel size is 4.64 µm and  resolution 0.67 arcsec/pixel.  PhD guiding software reported an RMS of 0.62 pixels in RA, 0.91 pixels in DEC and 1.10 pixels total.  Polar alignment error was 0.7 arc-minutes.

Image Processing

Final image comprised of 29 RGB images and 103 narrowband frames with an exposure of 180s.  Integration time for final image was 6 hours, 36 minutes.   PixInsightWBPP used to calibrate, register, align, and stack the subframes and create a 2X drizzled version which was then used to create this image.  Full Width Half Maximum (FWHM) width of the stars in the raw (undrizzled) image was 4.59 pixels.

I huge "thanks" goes to five software gurus who have developed PixInsight tools which make image processing easier:

1. Frank Sackenheim - developer of the stand-alone GraXpertAI application for removing background gradients.
2. Russell Croman - developer of BlurXTerminator, StarXTerminator, and NoiseXTerminator scripts for PixInsight.
3. David Payne and Michael Cranfield  - developers of the Generalized Hyperbolic Stretch script for PixInsight.
4. Michael Cranfield and Bill Blanchan - developers of Screen Stars and NarrowbandNormalization (and many other) scripts for PixInsight.

Sub-frames were calibrated, delayered, registered, and stacked using PixInsight's Weighted Batch Pre-Processor (WBPP) script, including 2X drizzled version.  GraXpertAI was then used to remove the background gradient (30%Bg/2sigma stretch and 0%smoothing AI settings).  Next, PixInsight’s Spectro-Photometric Color Calibration (SPCC) script was used to calibrate the color and neutralize the background.  BlurXTerminator was then applied to improve the details in the nebula and star shape (star reduction and halo settings were set to 0% and "correct first" option was used with a PSF of 4.64 pixels).  StarXTerminator was used to create starless and starry versions while the images were still in their linear state, and Generalized Hyperbolic Stretch (GHS) was then used to stretch the images.   Histogram and Curves used to boost the contrast and saturation of the Ha and Oiii components of the starless image.  HOO color palette versions of the starless image were also created using the new NarrowbandNormalization script.   StarMask generated for stars and color saturation increased using curves.  The new ScreenStars script was used to add the RGB stars back onto the starless image.