Ground Based Testing of the GAIA Filters

We summarise the case for ground based testing of the GAIA filter system. Two scenarios are evaluated; firstly, that ground based testing be part of the (ongoing) filter design effort, and secondly that the filters be tested on real stars from the ground after they have been finalised. We conclude that the filter design effort would benefit more efficiently and directly from good flux calibrated spectra for representative stars of many types, rather than an immediate and concerted ground based photometric effort. Ground based observations after the filter design has been frozen is highly recommended. We review an initial study of the tolerances needed on the filter central wavelengths and bandwidths in manufacture, assuming millimagnitude photometry. Further work is needed in this area. This revised version was published online in July 2006 with corrections to the Cover Date.