Location accuracy limitations for CCD cameras

The accurate measurement of the position of celestial objects is a fundamental step forseveral astrophysical investigations. For ground based instruments, the atmosphere is considered the basic limiting factor; in space, the knowlwdge of the instrumental parameters and/or their stability define the performance limits, but CCD cameras operated in time delay integration may take advantage of their operating mode to reduce significantly the calibration problem. We implemented a low cost laboratory experiment aimed at assessing the precision achievable in the location determinationwith a CCD camera, by evalueting the measurement repeatability throughout a set of images of a simulated stellar field. Our experiment provides an initial location dispersion of the order of 1/100 of the CCD pixel, with clear evidence of dominant common mode effects. After removing such terms with straightforward numerical procedures, we achieved a final location precision of 1/700 pixel on individual images, or 1/1300 pixel on co-added images. The scaling of precision with target magnitude is qin quite good agreement with theoretical expectations. The initial common mode systematics appear to be induced by the thermal control of the CCD camera head,which degrades the strctural stability. In actual implementations, such problems can be greatly reduced by proper design. Finally, our results show that residual effects, which could hamper the final astrmetric accuracy, can be calibrated out with simple procedures