CCD Astrometry of the Solar System

Bureau des longitudes, Paris, France

It can be said that the major event of the past 20 years in observational astronomy was the apparition of CCD detectors. Strangely, their impact in general astrometry was not so important mainly because astrometrists have the practice of large fields and that CCD chips are generaly not larger than a few square centimeters. However their high quantum efficiency and their linearity make possible new observation types. In the first part of this paper we will review special applications in the solar system astrometry; in the second part we will point out the use of the new catalogs (GSC, Hiparcos..) and at last we will prospect the future large field instruments.

1)

CCD detectors have shown their use in difficult observational conditions like when a bright objet pollute the sky background. In this case the dynamic and the linerarity of the device is irreplaceable. For this reason, the great successes of CCD observations were link to natural satellites observations. We can quote here the observations of faint satellites and of mutual phenomena of Jupiter ans Saturn satellites.

2)

The major drawback of CCD camera is their small size, so the astrometric calibration is always problematic because of the lack of astrometrical stars in the field of view. One way to get over this difficulty is to use GSC; this catalog is known to not be astrometric but it is now the only practible way to measure comet positions. The other way is to use close approaches between a solar sytem object and an astrometrical star. In this case calibration can be obtained thanks to the solar sytem object velocity and the global accuracy is linked to the knowledge of the star position which could belong to the Hipparcos catalog.

3)

CCD chip are now getting larger and larger, so it can be possible to use the `old astrometric' methods for most of the solar system objects. In this part we will review the existing and future instruments and their possible use for solar system astrometry.