Arp319
Arp319 | Stephan's quintet- Click here for full resolution
Stephan's Quintet, is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered. The group, visible in the constellation Pegasus, was discovered by Édouard Stephan in 1877 at the Marseille Observatory. The brightest member of the visual grouping (and the only non-member of the true group) is NGC 7320, classified in the Arp catalogue as Arp319, which has extensive H II regions, identified as red blobs, where active star formation is occurring. Four of the five galaxies form a physical association, a true galaxy group, Hickson Compact Group 92, and will likely merge with each other. Radio observations in the early 1970s revealed a filament of emission between the galaxies in the group. This same region is also detected in the faint glow of ionized atoms seen in the visible part of the spectrum as a green arc. Space telescopes have provided new insight into the nature of the filament, which is now believed to be a shock-wave in the intergalactic gas, caused by one galaxy (NGC 7318B) falling into the center of the group at several million kilometres per hour. Stephan's Quintet was selected as one of the five cosmic objects observed by the James Webb Space Telescope as part of the release of its first official science images.
source: wikipedia
NGC/IC:
Other Names:
Object:
Constellation:
R.A.:
Dec:
Transit date:
Transit Alt:
NGC7317, NGC7318, NGC7319, NGC7320
Stephan’s quintet
Galaxy
Pegasus
22h 36m 04s
+33° 56.0′
02 October
86º S
Conditions
Arp319 is best visible in late-summer and autumn time. Peak altitude in October 86°. Images were taken over eight nights throughout the month of July 2024 from the remote observatory at IC Astronomy in Oria, Spain.
Equipment
The default rig at the observatory was used. The core of this rig is a Planewave CDK-14 telescope on a 10Micron GM2000 mount, coupled to a Moravian C3-61000 Pro full-frame camera. The RoboTarget module in Voyager Advanced automated the process to find optimal time-slots during astronomical night.
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14, Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro, cooled to -10 ºC
Chroma 2” LRGB unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Windows 11, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.8.9-3
Imaging
The Arp catalogue is a very interesting catalogue with deep sky objects of unique morphology. NGC7320 itself is quite regular in structure, but it is in the line-of-sight of four additional galaxies, that make together for an exceptional object, known as Stephan’s quintet. A long focal length setup with the CDK14 is a good way of imaging them. But the full-frame camera is too much. Therefore the image here is cropped in to keep the focus on the quintet. Arp319 was captured using both Luminance (180s) as well as Red, Green and Blue (300s) broadband filters. A total of almost 20h of data was acquired.
Resolution (original)
Focal length
Pixel size
Resolution
Field of View (original)
Image center
4506 × 3096 px (13.9 MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
22' x 151'
RA: 22h 36m 0.790s
Dec: +33° 58’ 07.40”
Processing
All images were calibrated using Darks (50), and Flats (50), registered and integrated using the FastBatchPreProcessing (WBPP) script in PixInsight. A new set of flats was created, and a total of 50 flats was chosen as that was the outcome of some earlier testing as being a better option than the regular 25. A real difference is difficult to see, but for now I’ll just go with the 50. The rest of the processing followed a fairly standard pattern.
Any gradients were removed from the Red, Green and Blue channels before they were combined, colour calibrated (SPCC), and deconvolved (BXT). After colour calibration a very faint green gradient was visible in the image, which was removed by GradientCorrection in its default settings. Stars were removed and kept for later processing. The RGB image was treated with a bit of SCNR to remove a bit of green tint and stretched using several iterations of GHS, followed by some contrast and saturation enhancements using CurvesTransformation. Noise was removed with NoiseXTerminator.
Any gradient in Luminance was removed using GraXpert. Deconvolution (BXT) was followed by StarXTerminator to create a starless image and the stars were kept for later. The starless luminance was stretched using several iterations of GHS. Noise was removed (NoiseXTerminator) and sharpness was enhanced by LHE and Unsharpmask.
The RGB stars were stretched using the automated StarStretch script from SetiAstro. The blue had a slight touch of teal, which was pushed back to a real blue. Normally I would use just the RGB stars, but this time I decided to try to enhance them a bit more by combining them with the luminance stars. So the RGB stars were smoothened out using Convolution, luminance stars were stretched using the StarStretch script and both were put together with LRGBCombination. The stars looked good, but it would be hard to see a real difference with just using the RGB stars.
The starless luminance was added to the starless RGB image, and stars were put back in using the screening function in PixelMath. The background level was adjusted to 0.07 using BackgroundNeutralization, to align it with my other images. The original SPCC was done using S0 galaxy as the white reference. For this target, I felt that the white balance was just a bit too cold, so the reds were a bit boosted with ColourSaturation. A final crop was applied as the galaxies were looking quite small in the full-frame image.
Processing workflow (click to enlarge)
This image has been published on Astrobin and received Top Pick nomination status.
