How to create of images in natural colours with standard photometric filters.
Dumbbell nebula (M 27) is a planetary nebula in Saggita. Dumbbell is one from favourite objects for small telescopes, although its colours are unseen for visual observers except very large equipment.
A sample data are available as munipack-data-m27.tar.gz. Save it to arbitrary directory (for example /tmp/) like:
$ cd /tmp $ tar zxf munipack-data-m27.tar.gz $ cd munipack-data-m27/
The directory munipack-data-m27/ contains exposures in the instrumental colour system (nearly Johnson) in BVR filters and corresponding dark frames. B filter exposures has duration 60 seconds. Both V and R filter exposures has 40 seconds. Flat-fields are not available.
Follow these steps to get a colour image:
$ munipack dark -o d60.fits d60_*.fits $ munipack phcorr -dark d60.fits m27_*B.fits $ munipack dark -o d40.fits d40_*.fits $ munipack phcorr -dark d40.fits m27_*[VR].fits
$ munipack find m27_*.fits $ munipack aphot m27_*.fits
To check detected stars and its preliminary photometry, run xmunipack:
$ xmunipack m27_01R.fits
$ munipack cone -r 0.1 299.87 22.71
$ munipack astrometry -c cone.fits m27_*.fits
$ munipack kombine -o m27_B.fits --rcen 299.9 --dcen 22.72 m27_*B.fits $ munipack kombine -o m27_V.fits --rcen 299.9 --dcen 22.72 m27_*V.fits $ munipack kombine -o m27_R.fits --rcen 299.9 --dcen 22.72 m27_*R.fits
$ munipack coloring -c 'Johnson BVR' -o m27.fits m27_B.fits m27_V.fits m27_R.fits
The output image nicely shows regions where radiation of forbidden lines dominates (green) and Hα regions heated by shock-waves (red).
Also try how this image would be visible by human vision at night, when colour vision receptors (rods) is not activated. The appearance will be similar to visual sights. Use xmunipack and Tune->Color_menu or try helper utility:
$ fitspng -fn 0,1 -o m27.png m27.fits
Manuals: Coloring, Kombine, Astrometry, Aperture Photometry, Photometric corrections.
Tutorial: Image Compositions