IC4954 and IC4955
IC4954 and IC4955 - Click here for full resolution
IC4954 and IC4955 are two nebulae in the constellation Vulpecula. They are part of a much larger complex of newly formed stars. This much larger cluster is called Roslund 4 and it is estimated that the stars found here are 4 million years old. The very sharp boundary (shock front) between some of these stars and the molecular cloud serves as a chronometer for the cluster. It is unlikely that a structure like this, caused by the outflow of these energetic young stars, would persist for timescales longer than 6 million years. It is estimated that this star forming region is 6,000-8,000 light years away.
source: Noirlab
NGC/IC:
Other Names:
Object:
Constellation:
R.A.:
Dec:
Transit date:
Transit Alt:
IC4954, IC4955
Roslund 4
Nebula
Vulpecula
20h 04m 53s
+29° 11.5′
25 August
82º S
Conditions
IC4954/IC4955 can be well observed from during Summer, with maximum altitudes reaching 82° in the South. Unfortunately I started imaging this target in early October, which was a bit late. So shorter and shorter time-windows in the early evening were available to capture images. Weather conditions were not great either. So many nights either no observations could be made, or the resulting images were of such poor quality that they had to be discarded. In the end this image was captured over 20 nights, during the months of October, November and December 2024 from the remote observatory at IC Astronomy in Oria, Spain.
Equipment
The default rig at the observatory was used. The core of this setup 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 50mm Luminance, 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 1.9.2
Imaging
Capturing this image was inspired by a member of my local astronomy club, who explained the uniqueness of the Roslund 4 cluster. These targets are not photographed very often, and it is easy to see why. Their angular size is about 2 arcmin, and that is very small. A long focal length setup like the one applied here is a good instrument to capture them, but still it requires a heavy crop into the final image. Although the nebula are categorised as HII regions in some catalogues, the most common way to image them is using broadband filters. It was hard to gather the intended amount of 20h of exposure. As time progressed, the target moved out of the observable window quickly and visible and lower altitudes only. In combination with poor weather conditions at times, many of the sessions only had 0.5-1.5h of data collected. But just before the target would out of sight completely, all 20h of exposure was captured.
Interestingly the annotation in PixInsight using the Vizier database only picked up IC4954. It was hard to find the proper allocation as to which nebula carries which name. Most standard planetarium software does not have images available. Telescopius does, but not all images are annotated correctly. Simbad eventually revealed the proper name to the proper nebula. Using the DrawAnnotation script, the additional label was added to the annotated image.
Resolution (original)
Focal length
Pixel size
Resolution
Field of View (original)
Image center
2400 × 1800 px (4.3 MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
12' x 9'
RA: 20h 04m 50.517s
Dec: +29° 12’ 34.42”
Processing
All images were calibrated using Darks (50), Flats (50) and Flat-Darks (50), registered and integrated using the WeightedBatchPreProcessing (WBPP) script in PixInsight. This was the first time that the new version 1.9.2 of PixInsight was used. All further processing was done in PixInsight, including the use of scripts and tools developed by RC-Astro, SetiAstro, GraXpert, and others. For a step-by-step description of the processing techniques applied, see process flow below.
A key new tool in PixInsigh 1.9 is the MultiScaleGradientCorrection tool. Rather than applying some kind of mathematical analysis to discover gradients, MGC compares the image with a gradient-free reference image. These reference images are stored in the Mars-database. This database does not yet cover the complete sky, but the current target was covered. The tool worked very straightforward and a nice gradient-free image was the result. Only the flux calibration tool, which is a prerequisite for MGC to work, was not completely understood. The tool works with the specifications of the actual filters used. And most filters that are used today are in the list of options to choose from. For RGB this worked fine. Bu for luminance there were hardly any luminance filters in there. In my case for example, I used the Chroma Luminance filter, but listed in the tool are only the RGB filters under the luminance tab. In this case I reverted to the ‘Ideal QE curve’, but would like to understand a bit better why there are so few luminance filters in the tool.
The rest of the processing was pretty standard. Worthwhile mentioning is that the colour of the nebulae was a little increased. To protect the stars, a mask was created from a starless version.
There have been some early bugs in PixInsight 1.9, but using the current version 1.9.2 all processing was done without the software crashing a single time.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
