Arp41
Arp41 - Click here for full resolution
Arp 41 is a grand design spiral galaxy located in the constellation Eridanus, approximately 60 to 65 million light-years away from Earth. It is part of Halton Arp's Atlas of Peculiar Galaxies, a catalog of unusual and distinctive galaxies. Arp41 is a classic example of a grand design spiral galaxy, with well-defined spiral arms that are rich in young, hot, blue stars, as well as regions of active star formation. It includes a smaller, irregular companion galaxy, NGC 1232A, which appears to be interacting gravitationally with the main galaxy. This interaction may contribute to the enhanced star formation observed in Apr41's spiral arms. Arp41 spans about 200,000 light-years in diameter, making it roughly twice the size of the Milky Way. Its spiral arms are dotted with bright star clusters, nebulae, and dust lanes.
source: DeepSeek
NGC/IC:
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Object:
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R.A.:
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Distance to Earth:
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Tr. Alt (Oria, Spain):
NGC1232
n.a.
Galaxy
Eridanus
03h 09m 45s
-20° 34.0′
60-65 million ly
10.9
09 December
32º S
Conditions
Arp41 has a declination of -20°, and is therefore hard to image from the northern hemisphere. It is best visible during Autumn and Winter. But even during this time, when observed from the remote observatory at IC Astronomy in Oria , Spain, it never reaches any altitude much higher than about 30°. Typically I don’t image below 30° as the atmosphere is often not very transparent and causes too much distortions. for this target, there was no escape, so the software was programmed to image this target from 2h before the meridian, until 2h afterwards. This generally meant that the amount of imaging per session was very limited, resulting in a lot of sessions. Arp41 was photographed from the observatory in Spain over 16 nights, starting October 2024, all the way until mid February 2025.
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” 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
Arp41 is a typical broadband object, and the default exposure times were used. This means 3 minutes for luminance and 5 minutes for each of the Red, Green and Blue filters. The total exposure was almost 20 h. Due to the reported high level of star formation reported for this galaxy, some H-alpha exposures were made as well. However they did not pick up a whole lot of information, and given the challenging position of the target, it was decided to concentrate on an LRGB image only. Due to the fact that the target was often so low on the horizon, subs from many sessions were thrown away due to poor quality, so had to be re-taken. That became a bit of a race against the clock, as the target would soon run out of the observable window. The original plan was to have 5 more Blue subs, but as time had run out, it was decided to go with whatever was collected. A mild crop was applied to the final image to emphasise the galaxy’s structure.
Resolution (original)
Focal length
Pixel size
Resolution
Field of View (original)
Rotation
Image center
6000 x 4000 px (24 MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
30' x 20'
179.208°
RA: 03h 09m 45.297s
Dec: -20° 34’ 43.73”
Processing
All images were calibrated using Darks (50), Flats (50) and Flat-Darks (50), registered and integrated using the WeightedBatchPreProcessing (WBPP) in PixInsight. 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.
Processing followed a very standard pattern. To maintain colour in the RGB image, GHS stretching was performed in the ‘Colour’ mode. A simple increase in saturation after stretching was enough to create the right level of colour nuances.
Processing workflow (click to enlarge)
This image has been published on Astrobin
