<b>Field 3</b>: Satellite target in case of a joint entry

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Field 3: Satellite target in case of a joint entry

While the location of the `satellite target' (the part of the sky on which the detector is centred for the particular observation) is well defined for single stars, being the best estimate of the star's position at the epoch of the satellite observation, the situation is not so straightforward for double or multiple systems. For such systems, the choice of the target position may be:

[]The nature of the target for the satellite observation depends upon the separation and difference of magnitudes between the components, and has been dictated by considerations of the observation and data reduction procedures (Turon et al. 1989b). The brighter component is chosen when the signal perturbation due to the other component(s) can be neglected ( mag). For mag, there are two possibilities according to the geometry of the system and the availaibility of data for the components. The geometric centre has been selected when the positions and magnitudes of each component are known. A `geometric centre' may also have been adopted for some multiple systems when the two brightest components dominate the other components. The photocentre has been selected if the separation is such that only one position or magnitude has been obtained for the system as a whole, or in the case of multiple systems. When the component separation is smaller than 3 arcsec, the entry is considered as a photocentre irrespective of the difference of magnitude between the components.

The Meudon Hipparcos Input Catalogue Team
mer 16 nov 15:51:31 MET 1994