NGC7331 and the Deer Lick Group


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August 7, 2013

NGC7331 is in Pegasus, and is about 50 million light years away.  The smaller galaxies around NGC7331 are around 10 times further away, or 500 million light years (yes, half a billion light years!).  Collectively, this is referred to as the Deer Lick group of galaxies, but I find “the Mosquito Group”  to be more apt.  At least I would relate to the imagery — the little galaxies around the big one are kind of like mosquitoes buzzing around me looking for a meal.  There are many galaxies scattered throughout this image; some are very small and faint (look for little streaks, fuzzy-looking “stars” and faint “stars” that seem to have a slight fog around them).

This was an interesting image to acquire and process.  All the colour data was captured a couple of years ago with a different camera and scope setup, and the brightness (luminance) data was acquired in the last few weeks.  At 13 hours, I think this is my longest total exposure to date.  Hope you like it!


Acquisition, guiding, calibration, registration and integration all done using Maxim-DL.  All other processing in PixInsight.  Shot from my SkyShed in Guelph, Ontario.   Acquisition took place at two different time periods (summer 2013 for luminance and autumn 2011 for colour).  Two different cameras (QSI583wsg and SBIG STL-1000M) and focal lengths (900mm and 1700mm) were used.

LUMINANCE (SUMMER 2013):  48x10mL unbinned (total=8 hr).  SBIG STL-11000M camera, Baader LRGB filters, 10″ f/6.8 ASA astrograph, MI-250 mount.  Guided with STL-11000’s external guider and 400 mm f.l. guide scope.  No moon for L; moderate moonlight for RGB.  Average transparency and average seeing for RGB acquisition; good for L acquisition.  The luminance image was processed in PixInsight as follows:  DBE, Deconvolution, Histogram Stretch, HDR Multiscale Transform (6 and 6 layers), TGV Noise reduction, Unsharp Mask and slight convolution on the stars. The image scale for the luminance data is about 1.1 arcsec/pixel.

COLOUR DATA (from November 25 2011):  33x5m L, 25x2mL, 6x5m R, 5x5m G and 6x5m B unbinned frames (total=5 hr). QSI583wsg, Astrodon LRGB filters, 10″ f/3.6 ASA astrograph, MI-250 mount.  Guided with a SX-Lodestar guide camera using the QSI off-axis port.  The 2m L frames and all the RGB were shot with plenty of moonlight in the sky, and poor to average transparency.  The 5m L frames were shot under a clear, transparent sky with no moon and decent seeing (steadiness).  The LRGB image was created in Maxim-DL using the “Stack” command.  PixInsight was then used as follows:  First made an RGB image using the 2m L frames plus the RGB channels, using a standard workflow (Dynamic Background Extraction, Colour Balance, Stretch, ACNDR noise reduction, reset black point, saturation, masked sharpening).  I then separately processed the stack of 5m L frames using a similar work flow.  Then I registered the L and RGB images and applied the L to the RGB.  A slight saturation tweak was all that was needed to finalize the image.  Image scale for colour data is 1.23 arcsec/pixel.

COMBINING LUMINANCE AND RGB:  After realigning and cropping, Luminance was added to the RGB using the LRGBCombine tool in PixInsight with Chrominance Noise Reduction on.  A slight adjustment was made to luminance curve and to saturation.  Final image scale is 1.1 arc sec/pixel (the scale of the luminance data)

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