Flux standard data and empirical throughput

The figure below shows the results of throughput measurements of flux standards with the EEV12 and RED+ detectors in the blue and red arm respectively, and the 5300 dichroic. The Y-axis is the apparent AB magnitude of a star observed at the zenith which gives one detected photon per second per Angstrom. The lowest resolution grating (R158R) was used in the red arm (without any order sorter filter) and the R300B grating was used in the blue arm. Spectra were obtained with a wide slit (10 arcsec). Conditions were photometric, with negligible dust levels present.

The figure shows the total response of the ISIS blue and red arms (i.e., of the WHT primary and secondary, the 5300 dichroic, ISIS optics and the detector responses) over the spectral range ~3200 to ~9300Å. The dip in throughput centred on ~5300Å is of course caused by reduced throughput at the dichroic cross over from reflection (blue arm) to transmission (red arm).