The preparation of input catalogs for wide-field multi-object spectroscopic systems has turned out to be a non-trivial problem. With typical optical fibre diameters of 2 arcsec, the total errors in the input positions should not exceed 0.5 arcsec, otherwise significant light losses will occur. While it is not too difficult to measure positions with local internal accuracies corresponding to 0.1 -- 0.2 arcsec on Schmidt sky survey photographs, it is harder to translate these from one X,Y coordinate system into RA and Dec and then into another X,Y system. This accuracy has to be maintained across several degrees, and over the wide range of magnitudes needed to tie relatively bright guide stars to faint program objects. Problems arise from the large-scale distortions of Schmidt plates, from image profiles which vary with position and magnitude, and from proper motions. Two particular issues will be addressed: the establishment of a few very accurate high-density fields needed to test and calibrate the performance of the Two-degree Field (2dF) robot positioner on the Anglo-Australian Telescope; and the provision of guide stars with 13 < V < 16 for any two-degree diameter field in the southern sky.
IAU Joint Discussion
- Pub Date: