The APM Sky Catalogues: Catalogue Interrogation

We have found that the most common requests for use of the catalogue are: for optical identification projects (eg. given a radio target what is the most likely optical ID); producing finding charts of the sky for aiding observing at the telescope; producing lists of images near target positions for use in either finding guide stars, or in slit spectroscopy, for finding stars to use as reference images for blind offsets onto 'invisible' targets; as a source of accurate image positions for fibre spectroscopy; and as a means of providing faint secondary astrometric standards for bootstrapping astrometry onto CCD frames.

Although the preceding list should be taken as illustrative rather than exhaustive there are two common themes in these uses; the ability to produce a 'picture' of the sky (finding chart) and a means of producing lists and properties of all images in a specified area (searching). To facilitate catalogue queries we have therefore installed a restricted access account on the microVAX 4000 VLC where the catalogues reside and provided it with the means to take an input list of target coordinates (ra,dec) and produce one or both of finding charts and image lists. These can then be copied back to the local host machine for producing hardcopies etc.. The account is deliberately designed for use with a small number of targets and automatically partitions the target list into suitable field/plate centres. Details of how to access the account are given below.

Mike Irwin

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