Caldwell 51
IC 1613
47’ x 31’ | 0.3”/px | 9480 × 6260 px | full resolution
Cetus
RA 01h 04m 44s Dec +02° 08’ 51” | 0°
Caldwell 51, also known as IC 1613, is an irregular dwarf galaxy located on the outskirts of the Local group (the galaxy ground that includes our Milky Way) around 730 kiloparsecs from Earth in the constellation of Cetus near the star 26 Ceti. It has a low mass with its mass only being around 10^8 solar masses. It has played an important role in the calibration of the Cepheid variable period-luminosity relation for estimating distances. Other than the Magellanic Clouds, it is one of the few Local Group dwarf irregular galaxy where RR Lyrae-type variables have been observed; this factor, along with an unusually low abundance of interstellar dust both within IC 1613 and along the line of sight enable especially accurate distance estimates.IC 1613 was discovered in 1906 by Max Wolf, and is approaching Earth at 234 km/s.
source: Wikipedia
Data Acquisition
Data was collected over 9 nights during October and November 2025, using a 14” reflector telescope with full-frame camera at the remote observatory in Spain. Data was gathered using standrad LRGB filters and to highlight the areas of active star formation, enhanced with Ha signal. A total of 30 hours of data was combined to create the final image.
Location Remote hosting facility IC Astronomy in Oria, Spain (37°N 2°W)
Sessions
Frames
Equipment
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14 (2563mm @ f/7.2), Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro (full frame), cooled to -10 ºC
Chroma 2” LRGB, Ha (3nm) unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.9.3
Processing
All processing was done in Pixsinsight unless stated otherwise. Default features were enhanced using scripts and tools from RC-Astro, SetiAstro, GraXpert, CosmicPhotons and others. Images were calibrated using 50 Darks, 50 Flats, and 50 Flat-Darks, registered and integrated using WeightedBatchPreProcessing (WBPP). The processing workflow diagram below outlines the steps taken to create the final image.
An an irregular dwarf galaxy, a standard LRGB image of C51 does not show a lot of detailed structures, other than a colourful and busy star field. It is the Ha signal that really adds some great detail in the image and that showcases areas of active star formation. There are different ways to add Ha to an LRGB image and in this case the method of continuum subtraction has been applied. Details of how this method works can be found in the processing of M51. Using Imageblend to put it all together allows fine control over how the Ha will show up. I chose a hue of 298, to give it a bit of the pink hue that is often seen in such images.
Apart from the continuum subtraction, the main image was fully processed in the presence of the stars. As there is not a whole lot of non-stellar structure, this seemed the best approach. The Ha blending was done with a starless Ha image. The resulting ‘pure Ha’ image had quite a bit of a halo left from HD6375. To not have this interfere with the later blending, I decided to remove this part from the Ha image using the CloneStamp tool.
The rest of the processing followed a pretty standard processing workflow, as shown in the overview below.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
