Other
Scientific paper
Sep 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984msngr..37...36s&link_type=abstract
The Messenger, No. 37, P.36, 1984
Other
2
Scientific paper
The use of charge-coupled device (CCD) cameras in galaxy photometry offers a number of significant advantages over traditional photoelectric and photographic techniques. CCOs have a high quantum efficiency compared to photographic plates, and their response is linear over a large range of brightness. Since they are two-dimensional detectors, the centring problems of photoelectric photometers are avoided, and object and sky can be observed simultaneously. Of course, there are also some disadvantages; the CCD is much smaller in area than a photographie plate, and the read-out noise is a limiting factor for short exposures. However, one area in which CCD detectors are particularly valuable is in studying the inner regions of nearby galaxies, and in particular the colours and colour gradients in galactic nuclei. Here, the smaller size of the CCD is no disadvantage as we are studying objects 1-2 are minutes in angular size. Since the luminosity profile of a galaxy rises sharply towards the centre, saturation effects and the non-linear response of the emulsion present problems for photographie work, while it is extremely hard to obtain photoelectric aperture photometry with diaphragms smaller than 10-15" because of the difficulty in centring the galaxy accurately. The resolution of the GGO image, on the other hand, is limited only by the pixel size (0"47 at the Danish 1.5 m telescope) and the seeing (usually 1-2" at La Silla). This allows us a fascinating glimpse into the innermost regions of many nearby galaxies, and may provide new insight into the mechanisms responsible for "active" nuclei in galaxies.
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