Recently, I have been dealing a lot with detailed steps in image processing and also got to know new tools. With large, bright objects, smaller errors in the processing are not so easily noticed; these are simply more „tolerant“ in terms of processing. But when it comes to very faint objects, image processing becomes correspondingly more difficult.
The planetary nebula HDW 3, which was discovered by Austrians in 1983, is now a good example of how to implement all these new findings in the course of extensive image processing.
I will do this image processing very slowly and thoroughly and therefore probably use several parts of this article for it. First, I start with the easiest task, namely to process the 3-hour exposure time for the correct display of the stars with the filters in Red, Green and Blue. In the course of this work, I noticed a small galaxy about which I wanted to know more. Accordingly, I also documented how and where to get information about it, what helpful tools are available for this and how to approach further interesting facts from individual data.
A total of 16 hours and 50 minutes of exposure time was invested in the capture of the faint planetary nebula HDW3. In H-alpha it was 8 hours 15 minutes, in O-III 5 hours 35 minutes and finally one hour each in R, G, B was taken to map the stars correctly.
1. Processing RGB-stars
In the following, I summarise the processing steps in PixInsight that were carried out for editing the star images in the red, green and blue filters.
- Blink-Tool to sort out
- WBPP-Skript for R, G, B (calibration, normalisation, integration)
- SetiAstro`s AutoDBE (Gradient Correction) which includes the processes:
- AutomaticBackgroundExtractor
- DynamicBackgroundExtraction
- LinearFit (before the channels were analysed with the Statistics-Tool in order zu find out the reference channel – in my case it was the Blue-Channel with a mean brightness of 1.230 (Red was 870, Green was 1.157).
- BlurXTeriminator (a deconvolution tool from RC Astro)
- HistogrammTransformation (Stretching the images)
- NoiseXTerminator (RC Astro)
- SpectophotometricColourCalibration (SPCC) for correct star colors
- Colour Saturation
The tiny Galaxy …
While removing the noise, I noticed a tiny galaxy to the left below the centre of the image, basically just a small, narrow, orange-shimmering bar of about 30 arcseconds in length.
How can we find out what object is involved and what data is available or can be calculated? SetiAstro offers a (free) tool called ‘What’s in my Image’ that allows you to do initial research (linked to databases) directly out of PixInsight. First, I determined the size using also a free script named AngularDistance Script 1.1.1, created by Enzo de Bernardini and got about 30 arcseconds as a result.
The name of the object was thus found to be „2MFGC 2869“ and also the first data: diameter 0.527 (obviously in arcmin), type ‘G’ so a galaxy with the coordinates RA 52.174836 and Dec 45.342865. The brightest star in the image section is TYC 3312-535-1, a star of magnitude 11.5 mag. The advanced search function in PixInsight then takes one directly to the Simbad catalogue and the basic data of the galaxy:
I finally found the last details in the LEDA database. There, the galaxy is listed under the name PGC2263356 and further data is available. In the NED (NASA/Ipac Extragalactic Database), my depth of information finally ended.
Among several specifications, the redshift of 0.03111 can be found in the databases, which can be used to make a rough estimate of the distance:
From Redshift to the Distance
The redshift (z) of a galaxy is a fundamental measure used in cosmology to determine its distance from Earth. Redshift occurs due to the expansion of the universe, which stretches the wavelength of light emitted by distant galaxies. This phenomenon is described by the formula:
where λobserved is the observed wavelength and λemitted is the originally emitted wavelength. The redshift increases as galaxies move further away due to the expansion of the universe (Hubble). For small redshifts (z < 0.1), the distance to a galaxy can be approximated using the Hubble’s Law:
- c is the speed of light (299,792 km/s),
- H0 is the Hubble constant (≈70 km/s/Mpc),
- z is the measured redshift.
For our galaxy, with a redshift of 0.03111, this gives a distance of about 133 MegaParsec (MPc), or 133 x 3.26 = 434 million light-years.
Imagine?
Obviously, it is no longer possible to imagine a distance of that anymore. If one considers that our Milky Way has a diameter of about 100,000 light-years, the distance of the galaxy 2MFGC02869 would be 4340 times this diameter… 170 times the distance to the „nearby“ Andromeda Galaxy … and yes of course, all these attempts at an imagination must fail miserably too, …as the dimensions of the universe stretch beyond the grasp of our imagination.
