Quality Control and
Data Processing

The OmegaCAM shutter test is executed roughly every 90 days. It consists of four dome flats of 10 and 0.1 seconds with the shutter travelling in one direction, and the second dome flat pair (again 10 and 0.1 second exposures) is made with the shutter blades travelling in the other direction (up and down). The pipeline divides each long exposure by its corresponding short exposure, normalizes the result, and then averages along the row direction (i.e. perpendicular to the direction of shutter travel along the axis of the 8 OmegaCAM CCDs) resulting in two fits table files with the average flux level in each of 16,384 row pixels. Any differences in the two dome flat ratios can be attributed to an inhomogeneity in the travel speed of the shutter blades.

The pipeline creates two output frames from its shutter test recipe (omega_shutter): a 1 x 16,384 pixel row average of the shutter travel direction SHUTTER_UP (OC_PSHU_<DATE>_1_1_normal_normal.fits) and a 1 x 16,384 pixel row average of the shutter travel direction SHUTTER_DOWN (OC_PSHD_<DATE>_1_1_normal_normal.fits)

No health check plots are created for the shutter QC parameters.

Any inhomogeneity in the shutter travel in either direction will result in a ratio of the row averages (black line in QC report) having a significant slope. Furthermore, the comparison with the reference traces will be apparent. Shutter timing homogeneity must be better than +/-0.2% at exposures of 1 second.

History

The OmegaCAM shutter timing has been very stable and homogeneous.