M27 - Dumbbell Nebula
M27 - Dumbbell Nebula - Click here for full resolution
Messier 27 is a planetary nebula in the constellation Vulpecula, at a distance of about 1360 light-years. It was the first such nebula to be discovered, by Charles Messier in 1764. It has a brightness of visual magnitude 7.5 and diameter of about 8 arcminutes. Like many nearby planetary nebulae, the Dumbbell contains knots. Its central region is marked by a pattern of dark and bright cusped knots and their associated dark tails. The knots vary in appearance from symmetric objects with tails to rather irregular tail-less objects. Similarly to the Helix Nebula and the Eskimo Nebula, the heads of the knots have bright cusps which are local photoionization fronts.
source: Wikipedia
NGC/IC:
Other Names:
Object:
Constellation:
R.A.:
Dec:
Transit date:
Transit Alt:
NGC6853
Dumbbell Nebula, Apple Core Nebula
Planetary Nebula
Vulpecula
19h 59m 36s
+22° 43.2′
23 Aug
75º S
Conditions
M27 is a great target for summer, early autumn, with peak altitudes of 75° in August. Images were taken on 11 nights from mid July until early August 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, 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
Planetary nebulae are often great targets for narrowband imaging, and M27 is no exception. Both in the Ha and OIII emission lines, a lot of structure is visible. The core of the nebula is very bright and can be imaged with relatively short exposures. But the goal here was to also attempt to capture the much fainter radiations pointing outwards. So regular 10 min narrowband exposures were taken for both Ha and OIII. For proper star colours, some quick RGB data was collected. A total of almost 32 hours of data was acquired.
Resolution (original)
Focal length
Pixel size
Resolution
Field of View (original)
Image center
9414 × 6228 px (58.6 MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
47' x 31'
RA: 19h 59m 34.847s
Dec: +22° 43’ 21.78”
Processing
A lot of frames had been acquired, but not always under the best conditions. SubframeSelector was used to discard 13 frames, based on bad eccentricity and/or FWHM values. All remaining images were calibrated using Darks (50), Flats (25) and Flat-Darks, registered and integrated using the FastBatchPreProcessing (FBPP) script in PixInsight.
It was a big challenge to bring out the faint structures while keeping enough detail in the bright core of the nebula. The dynamic range in the original image is enormous. All sorts of HDR techniques were tried, but without the desired effect. This included GHS, HDRComposition, CreateHDRImage and HDR tools in Photoshop and Affinity Photo. Ultimately the best results I was able to get was with the script iHDR from Uri Darom. The way the script works is to first stretch to the maximum level you want the brightest areas to be. Then you run the script to bring out the fainter areas. There are various parameters that can be adjusted, but the easiest option is to choose one of the three presets. In many cases the Medium HDR might be enough, but for this image, High HDR gave the best results.
The iHDR script from Uri Darom gave the best HDR results and was relatively easy to use.
The HDR technique described above worked best by working on both Ha and OIII channel separately. So each channel was individually prepared using GraXpert, BXT and SXT and stretched using a combination of HT and GHS. Then iHDR was applied followed by some fine-tuning with CurvesTransformation, including a little bit of sharpening and noise reduction.
The HOO image was created using ChannelCombination. NarrowbandNormalization (HOO, lightness off, Mode 2, Blend 0.35, OIII boost 1.5, highlight reduction 1.3) was used to create the typical HOO palette, where the choice for a more intense blue as opposed a teal colour was a deliberate one. Colours were boosted a bit further with CurvesTransformation.
The stars followed a pretty standard pattern of removing background gradients, combining the image, calibrate colour, sharpen up with BXT and extracting stars out of the RGB image. Stretching was done using StarStretch from SetiAstro (amount 5, colour boost 1.2).
The final image could now be assembled, using PixelMath, adjusting background signal to 0.07 to align with my other images, and a last bit of mild noise reduction.
Processing workflow (click to enlarge)
This image has been published on Astrobin and received Top Pick status.
