The charge-couple device (CCD) camera has opened up many new possibilities for the amateur and professional astronomer.1, 2 The study of double stars has also benefited from the advent of the CCD camera. The measurement of position angle, separation, and magnitude can all be derived from a single short (few seconds) exposure with the CCD camera. With a typical camera available to the amateur and a 20-cm telescope (see Fig 16.1), pairs as faint as V = 16 can easily be measured. The increased sensitivity of the camera to light allows pairs much fainter to be measured than would be possible visually or photographically.
Like most innovations, there are some drawbacks and limitations inherent with this technology. Visual double star pair measurements taken with a micrometer are complete at the time of observation, but this is not the case with a CCD. After the image is taken with a CCD, then the processing of the images begins. In the simplest case, reasonable measurements of three quantities, position angle, separation, and magnitudes can be obtained from images that have no post observation processing. If your measurements require the most accuracy available from the image then more elaborate processing is required. The most accurate measurements require the observer to be knowledgeable, though not an expert, in techniques of astrometry and photometry.
The purpose of this chapter is to give the observer guidance in using a CCD camera to take double star measurements. As it is with most things, those individuals that are diligent in learning and experimenting with the telescope and camera can reap double star measurements that are both rewarding to the observer and of scientific value.
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