NGC6946, The Fireworks Galaxy
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August 17, 2013
I’ve imaged this before. I added more than 3 hr through a clear (uncoloured) filter to about 10 hours shot previously through clear, coloured and hydrogen-alpha filters. In this mashup, the older image data was used solely for colour information, with all the brightness information coming from the new data.
This galaxy’s common name is the Fireworks Galaxy, and it’s easy to see why. The reddish highlights are star-forming regions, similar to the Orion Nebula in our own Milky Way galaxy. This galaxy is more than 20 million light years away. We see it face on, so it’s possible to see lots of dark dusty lanes between the blue arms full of stars. In addition to looking like a fireworks display, this galaxy has acted like one: there have been 9 supernova explosions observed in it since 1917. It would be even brighter if it wasn’t so heavily obscured by our own galaxy’s dust lane. There’s likely a black hole gobbling up stars concentrated in the bright core of the galaxy. At 22 million light years away, it’s just a stone’s throw as far as galaxies go.
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) were used. Shot with ASA 10″ f/6.8 astrograph (luminance and some of the colour) and an 8″ f/8 RC. Total imaging time is 13hr 20m.
LUMINANCE (SUMMER 2013): 20x10mL unbinned (total=3hr20m). SBIG STL-11000M camera, Baader LRGB filters, 10″ f/6.8 ASA astrograph, MI-250 mount. Guided with STL-11000’s internal guider. No moon. Average transparency and average seeing. The luminance image was processed in PixInsight as follows: DBE, Deconvolution, Histogram Stretch, HDR Multiscale Transform (6 and 4 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 (July 2012; total of 10 hrs of data): H-alpha data acquired as follows: 12x20m Ha all acquired unbinned with a QSI583wsg camera, Astrodon 5nm Ha filter and RGB Gen-2 filters, and an 8″ f/8 RC on a MI-250 mount, from my SkyShed in Guelph. No cloud, average transparency and average seeing. MaximDL was used for acquisition, guiding, calibration, alignment and stacking. A QHY5 camera was used to guide through the QSI’s guide port. An LRGB frame was acquired as follows: 6x5m of R, G and B and 11x10m L were used to make an LRGB image. SBIG STL-11000M camera, Baader LRGB filters, 10″ f/6.8 ASA astrograph, MI-250 mount. Guided with STL-11000’s external guider and a 500mm f.l. Lumicon guide scope. Acquistion, guiding, calibration, registration and integration all done using Maxim-DL. Shot from my SkyShed in Guelph, Ontario. Ha was shot with nearly full moon. LRGB was shot with a first quarter moon. Transparency and seeing were average. Additional Luminance data was acquired as follows: 18x10m L was separately combined into an L image using same equipment and under the same conditions as the LRGB. LRGB, Ha and L images were cleaned up in PixInsight with DynamicBackgroundExtraction, and then registered and cropped. The HaRGBCombine script was then used to combine Ha and LRGB images. Colour calibration was applied followed by convolution, histogram stretch, HDR multiscale transform, ACDNR (small scale), histrogram stretch, ACDNR (large scale), histogram stretch, LocalHistogramEqualization (masked), curve, saturation, morphological transform on stars. Then the separate L frame was processed using a similar workflow and combined with the HaLRGB using the LRGBCombine command in PixInsight. A little stretching and colour balancing completed the processing. Image scale is about 1.1 arcsec per 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. Local HistogramEqualization was applied to the galaxy, TGV noise was applied to the background. Adjustment was made using curves (to increase contrast and brightness) and colour saturation (decreased in background). A morphological transformation was applied to shrink the stars slightly. Final image scale is 1.1 arc sec/pixel (the scale of the 2013 luminance data).