These pseudo-apertures are the same physical aperture as the 52X2
aperture, but are used to place the target at different locations on the detectors to reduce CTE loss or FUV-MAMA
background. The throughputs of the E1 and D1 apertures as a function of wavelength are similar to those of the corresponding regular positions. However, there is some vignetting of the gratings that changes the overall system throughput slightly with varying position along the slit. At the E1 positions, the overall low dispersion throughputs are decreased by 2 to 3%, while at the D1 position the G140L
throughput is increased by 2 to 7%. Throughput changes for the medium resolution gratings are not well characterized, but should be similar. Since these throughput changes depend on the grating and the position on the detector, they are handled in the pipeline calibration by the use of low-order flat fields (lfl files) rather than by a change in aperture throughput curve. Throughput at the 52X2E2
position is very similar to that at the 52X2E1
position. The usage of these slits is supported only for certain modes, as listed in the table below.
Same special considerations as for the 52X2
aperture apply to these pseudo-apertures. See reference information on previous page.