NGC 7331 and Supernova SN2025rbs
Click image for full size version
August 26, 2025
NGC 7331 is the largest galaxy in this image. It is located in Pegasus, and is about 40 million light years away, and has a diameter of about 120,000 light years. It is the biggest member of the “Deer Lick Group,” several other members of which are strewn around (mostly to the right of) NGC 7331. These galaxies are about 10 times further away, or 500 million light years (yes, half a billion light years!). See the annotated image which identifies most of the galaxies. I have imaged this galaxy in a wider field of view; you can find it here.
The above image also shows a supernova very close to the centre of NGC 7331. It was discovered on July 14, 2025. It is marked with an arrow in the image below (click for full size).
Tekkies:
Acquisition, focusing, and control of Paramount MX mount with N.I.N.A., TheSkyX and PHD2. Primalucelab low-profile 2″ Essato focuser and ARCO rotator. Guiding with PHD2. Equipment control with PrimaLuce Labs Eagle 4 Pro computer. Flats taken using a Primalucelab Giotto 430 mm flat panel. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Data acquired under variable moonlight with average or better transparency and and average seeing between August 13-16, 2025.
Celestron 14″ EDGE HD telescope at f/11 (3,912 mm focal length) and QHY600M camera binned 2×2 with Optolong filters.
51 x 5m Red = 4hr 15m
52 x 5m Green = 4hr 20m
50 x 5m Blue = 4hr 10m
24 x 5m Ha = 2hr 0m
Total: 14hr 45m
Preprocessing: The WeightedBatchPreProcessing script was used to perform calibration, cosmetic correction, weighting, registration, integration and Drizzle integration of all frames (1x drizzle, 0.9 Drop Shrink).
RGB and SynthL masters: A master RGB image was made from the Red, Green and Blue Drizzled masters using ChannelCombination in RGB mode. A synthetic luminance (SynthL) master was made from all four masters using ImageIntegration with weighting by SNR.
Gradient Removal: DynamicBackgroundExtraction was applied to the SynthL, RGB and Ha masters.
Colour Calibration: BlurXterminator was applied to the RGB master with Correct Only selected, followed by ColorCalibration.
Deconvolution: BlurXterminator was applied to the RGB, SynthL, and Ha masters with Automatic psf , star sharpening set to 0.5, and non-stellar set to 0.9.
Linear Noise Reduction: NoiseXterminator was applied to the RGB, SynthL, and Ha masters with settings Amount=0.9 and Interations=4.
Ha Continuum Subtraction: The SpectrophotometricContinuumSubtraction script by Charles Hagan was used to remove continuum emissions from the Ha master using the red channel of the RGB master as the continuum reference image.
Stretching: HistogramTransformation was applied to make a pleasing image from the RGB, SynthL, and Ha masters. Approximate background level after stretch was 0.1 for SynthL and 0.08 for the Ha and RGB masters.
Nonlinear Processing
Luminance-RGB addition: LRGBCombination was applied to replace the lightness of the RGB image with the Luminance master.
Star Removal and processing: StarXterminator was used to remove the stars from the LRGB and Ha masters with Unscreen checked. The Ha stars were discarded. Colour was increased in the LRGB stars-only image by applying Curves saturation through a star mask.
Initial Saturation Boost: CurvesTransformation’s saturation tool was used to boost colour in the galaxies in the starless LRGB image using a range mask made with RangeSelection to protect the background.
H-alpha Blending: The contiuum-subtracted Ha was added to the LRGB image using Jurgen Terpe’s CombineHaWithRGB script.
Nonlinear Noise Reduction: NoiseXterminator was applied to the HaLRGB image with settings Amount=0.9 and Iterations=5.
Contrast Enhancement: LocalHistogramEqualization was then applied twice. A Contrast Limit of 1.5 and 1 iteration was used for each application (scale 40, strength 0.2, and scale 150, strength 0.25).
Sharpening: MultiscaleMedianTransform was used to sharpen Layers 1 – 5 with strengths of 0.03, 0.03, 0.03, 0.04, and 0.01, respectively.
Star Restoration: Stars were added back into the image using the PixelMath expression combine(starless, stars_only, op_screen())
Final Steps: Background, galaxy, and star brightness, contrast, and saturation were adjusted in several iterations using ExponentialTransforamtion and CurvesTransformation with masks as required. ICCProfileTransformation (sRGB IEC61966-2.1; Relative Colorimetric with black point compensation) was applied prior to saving as a jpg. The finder chart was made using the FindingChart process. The annotated image was made with the AnnotateImage script.
Outstanding!!