M57
M57 or Ring Nebula- Click here for full resolution
Messier 57, also known as the Ring Nebula, is a planetary nebula in the northern constellation of Lyra. It is formed when a star, during the last stages of its evolution before becoming a white dwarf, expels a vast luminous envelope of ionized gas into the surrounding interstellar space. This nebula was discovered by the French astronomer Charles Messier in late January 1779. French astronomer Antoine Darquier de Pellepoix independently rediscovered the nebula independently two weeks later. Darquier later reported that it was "...as large as Jupiter and resembles a planet which is fading". This may have contributed to the use of the persistent "planetary nebula" terminology. In 1800, German Count Friedrich von Hahn announced that he had discovered the faint central star at the heart of the nebula a few years earlier. He also noted that the interior of the ring had undergone changes, and said he could no longer find the central star. In 1864, English amateur astronomer William Huggins examined the spectra of multiple nebulae, discovering that some of these objects, including M57, displayed the spectra of bright emission lines characteristic of fluorescing glowing gases. Huggins concluded that most planetary nebulae were not composed of unresolved stars, as had been previously suspected, but were nebulosities. The nebula was first photographed by the Hungarian astronomer Eugene von Gothard in 1886.
source: Wikipedia
NGC/IC:
Other Names:
Object:
Constellation:
R.A.:
Dec:
Transit date:
Transit Alt:
NGC6720
RingNebula
Planetary Nebula
Lyra
18h 53m 53s
+33° 01.7′
06 October
86º S
Conditions
M57 can be very well observed in Autumn and early Winter, with maximum altitudes reaching 86° in the South. Here, M57 was photographed over 7 nights during the end of September and early October 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” H-alpha, and OIII (both 3nm) and Red, Green and Blue 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
Often, the Ring Nebula is imaged in normal colours. An intense blue core and bright red ring are characteristic for such images. However, hydrogen-alpha emitting gasses extend well beyond the core of the nebula. Therefore M75 was imaged in narrowband, using the HOO-palette. It is a small target, so the long focal length of the CDK14 works well. The FoV of the full-frame camera is still too big though, so the final image was cropped in to a final field of view of 22x15 arcminutes.
Resolution (original)
Focal length
Pixel size
Resolution
Field of View (original)
Image center
4500 × 3000 px (13.5 MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
22' x 15'
RA: 18h 53 35.214s
Dec: +33° 01’ 42.20”
Processing
All images were calibrated using Darks (50), Flats (50) and Flat-Darks (50), registered and integrated using the WeightedBatchPreProcessing (WBPP) script in PixInsight. Stacking artefacts were removed using DynamicCrop. Individual colour channels were processed by gradient removal (GraXpert) and deconvolution (BXT).
Stars were removed from the individual Ha and OIII channels using StarXTerminator (SXT). Then the hard bit came. The OIII and Ha regions around the core Ring Nebula were really a lot fainter than the bright core. Regular stretching would never reveal the full details, so an HDR technique had to be applied. In previous images I had good experience using iHDR, so that was tried here. First both Ha and OIII were carefully stretched using GHS. It was stretched to the point that the bright core would have a value of approximately 0.7. Then iHDR was applied at its maximum setting. That really brought out nicely the clouds surrounding nebula core. The HOO image was then created and NarrowbandNormalization helped to pull out the red and blue colours. But given the large contrasts in the original image, also this appeared a lot more difficult than normal. Lots of pulling, pushing with the CurvesTransformation tool was needed to create the intended colours and contrast. Then noise was removed using NoiseXTerminator (NXT). After all this pulling, the core of the nebula had slowly gained some brightness again, slowly loosing its detail. This time another HDR tool was used, HDRMultiscaleTransform. It immediately pulled some nice details from the core of the nebula. A minor re-balancing of the colours using HistogramTransformation and a mild run of LocalHistogramTransformation to emphasise some structures gave the final desired result. A second run of noise reduction completed the HOO image.
The R, G and B channels were combined using ChannelCombination, then calibrated using SPCC. The stars were extracted (SXT) and stretched using the SetiAstro StarStretch script. This got the stars ready to be recombined with the main image.
The stars were added to the HOO image using CombineImages. BackgroundNeutralization was used to give the background a similar value as other images. However, with all the colour adjustments, the background had a bit of a red-cast over it, which was removed with a gentle push with HistogramTransformation. As the final step the image was cropped make the nebula stand out more.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
