TESTT/CCD

The command does a series of tests on a catalogue of flat frames. The flat fields in the catalogue should be grouped in pairs with the same exposure time. Most ideally, one should be two groups of 8 frames each - the first with increasing exposure times and the second with decreasing exposure times, interleaved with those of the first group. In this way, tends observed in the CCD response that are probably caused by the effect of temperature variations on the light source can be rejected.

The command requires a value for the mean bias level and the standard deviation in the keywords BIASMEAN and BIASSIGM to be filled and hence should be executed after the command TESTB/CCD. If no value or the value zero is found no bias offset will be subtracted. The command produces:

• A table containing the exposure time of the first of each sets (frames 1); the exposure time of the second frames (frames 2); the median pixel intensities over the selected frame sections in frames 1; the median pixel intensities over the selected area in frames 2; the variance of the difference of the frames 1 and 2
• Two linearity curves, expressed as count rate versus true exposure time. The mechanical shutter delay is determined either by linear extrapolation of the normal linearity curve (observed counts versus exposure time), thus assuming the response of the CCD is linear, or by adjusting the exposure times such that the count rate curve is closest to a straight line, thus allowing for a first-order nonlinearity in the response of the CCD.
• A transfer curve (Janesick et al., 1987) generated for any window onto the images obtained.