NGC7331 and Stephan’s Quintet

NGC7331 and Stephan's Quintet
Click image for full size version

SkyNewsOctober 19, 2014; published in January/February 2015 SkyNews Magazine (page 44

The big galaxy to the lower left of this image is called NGC7331.  It is the biggest member of the “Deer Lick Group”, several other members of which are obvious around (mostly beneath) NGC7331.  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!).  There are many other galaxies in this image, some are very small and faint (look for the fuzzy-looking “stars” and the faint “stars” that seem to have a slight fog around them).

To the upper right of the image is a group of galaxies called Stephanís Quintet.  Four of the five form an association about 290 million light years away, while the 5th one is much closer, at “only” 40 million light years.   The odd one out is the bluest of the grouping.  There is a beautiful tidal tail visible that looks like a little curl hanging off the bottom of the quintet.  I’ve seen Stephan’s Quintet several times visually through my 20″ telescope, but this image shows much more detail than I can see, and shows colour.  

The colour data from this image was used for a close up image of NGC7331 and the Deer Lick Group.

As I write this post, I am at a cottage in Muskoka, Ontario with my friends Gord (G1), Gord (G3), Gerry and Peter.  Gord (G2) couldn’t make it.  It is a grey and rainy day, but we are having a ball!

Tekkies:

LUMINANCE DATA (Oct 2014):  41x10m L (total 6hr50m).  SBIG STL-11000, Baader L filter, 10″ f/6.8 ASA astrograph, Paramount MX.  Guided with main camera’s remote guide head with a Stellar-Vue SV80 refractor.  Shot from my SkyShed in Guelph, Ontario. Excellent transparency, good seeing, no moon.  Acquistion and guiding with TheSkyX.  All preprocessing and pre-processing in PixInsight.  After combining the data, it was cropped to match the colour image.  Then the following processes were applied:  DBE, deconvolution, LinearMultiscaleTransform for noise reduction, HistogramTransformation,  HDR MultiscaleTransform (6 and 4 pixel scales), TGVNoise, HistogramTransformation, LocalHistogramEqualization, Curves.

COLOUR DATA (Oct-Nov. 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.  Shot from my SkyShed in Guelph, Ontario. 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).  Acquistion, guiding, calibration, registration, integration and initial colour balance all done using Maxim-DL.  PixInsight for everything else.  The LRGB image was created in Maxim-DL using the “Stack” command.  PixInsight was then used as follows:  First I 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 this camera/telescope combination is 1.23 arcsec/pixel.

COMBINING LUMINANCE WITH RGB:  The luminance channel was extracted from the colour image, matched to the high res Luminance image and then added back into the colour image using Lab mode in ChannelCombination.  Then LRGBCombine was used to add the Luminance to the colour image.  Saturation and contrast were tweaked.  Image scale isabout  1.1 arcsec/pixel.

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