NGC7129 Open Cluster with Nebulosity
Click image for full size version
August 20, 2013
I shot the colour data for this image in July 2011, and added 4 hours of brightness (clear filter) data that I acquired last week. I’ve attached the 2011 version of this object so you can see how much difference the added luminance data (and 2 additional years of processing experience) makes. Here’s what I wrote in my email in 2011:
Meet NGC7129, located in the constellation Cepheus. NGC7129 has two parts: an open cluster, and pretty surrounding nebulosity. The open cluster is a group of stars that formed together at around the same time, and they are gradually drifting apart. The nebula surrounding the cluster is of a few different kinds: emission nebula (red, due to glow of hydrogen gas), reflection nebula (bluish, due to light from the brightest stars reflecting off particles of dust around them, and dark nebula (the dark lanes in the core and in the area around the nebula that has relatively few stars, due to dust blocking the nebula’s light from our view). The cluster contains more than 100 stars, each less than a million years old — newborns by stellar standards. It’s also relatively close, at a little more than 3000 light years. I’ve read that he three bright stars in the nebula are kind of blowing a bubble in the middle of the nebula. While you’re enjoying the view of the nebula and star cluster, see how many galaxies you can find in this image. Start your galaxy hunt in the upper left corner.
One of my astro-buds teased me that I may have to go back and re-shoot everything I shot before… Well, if that’s what it takes, that’s what it takes!
By the way – to all who provide feedback, whether a word or a tirade, thank you! And to those who look but don’t write back — I hope you’re enjoying these pics. If you ever want to be removed from this list, you have but to ask!
All data: Acquired from my Sky Shed in Guelph. MaximDL was used for acquisition, guiding, calibration, alignment and stacking. No moon, no cloud, average transparency and average seeing for all nights. Total exposure time 13hr40m acquired over 6 nights between July 2011 and August 2013.
COLOUR DATA (SUMMER 2011): Twenty-minute unbinned frames were acquired as follows: R, G, B and Ha 2 hours each, and L 1 hr 20m. Total acquisition time was 9hr20m, acquired over 3 nights. QSI583wsg camera, Astrodon 5nm Ha filter, Astrodon LRGB Gen-2 filters, and an 8″ f/8 RC on a MI-250 mount, from my SkyShed in Guelph. A QHY5 camera was used to guide through the QSI’s guide port. All processing was done in PixInsight except the final step. Dynamic Background Extraction was applied to the Ha and RGB and L images. Then the red channel was extracted and modified by blending with the Ha data using Vicent Perris’ formula in PixelMath. The new red channel was combined with the original green and blue channels to make an HaRGB image. This was processed with Colour Balance, histogram stretch, masked sharpening, curves and noise reduction (masked, 2 different noise scales). Similar processing was performed on the L channel. The L was then added to the HaRGB image and saved as a 16-bit tif file. Photoshop was used for slight and selective sharpening with a high-pass filter layer blended using the soft light blend mode, heavily masked. Image scale for this telescope/camera combination is 0.68 arcsec/pixel.
LUMINANCE (SUMMER 2013): 26x10mL unbinned (total=4 hr 20m). SBIG STL-11000M camera, Baader LRGB filters, 10″ f/6.8 ASA astrograph, MI-250 mount. Guided with STL-11000’s internal guiderThe 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.
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. After TGV Noise reduction, Local Histogram Equalization was run on with a mask protecting everything but the nebula. A slight adjustment was made to luminance curve and to saturation. Exponential Transformation was applied to the background. Final image scale is 1.1 arc sec/pixel (the scale of the luminance data).