52X2E1, 52X2E2, and 52X2D1 Pseudo-Apertures


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 CCD CTE loss (E1 and E2) or FUV-MAMA background (D1). 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%. 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, only for the L-mode) rather than by a change in aperture throughput curve. Throughput changes for the medium resolution (M-mode) gratings are not well characterized, but should be similar. Throughput at the 52X2E2 position is about 20% lower than that at the 52X2E1 position. The usage of these slits is supported only for certain modes, as listed in the table below.

Special Considerations

Same special considerations as for the 52X2 aperture apply to these pseudo-apertures. See reference information on previous page.



Allowed Gratings




All CCD gratings

Places the target at row ~900 to minimize CTE effects



G750L & G750M

Places the target at row ~900 to minimize CTE effects; positions are offset from the center of the physical aperture in the dispersion direction, to give better alignment with fringe flats done using 52X0.1 aperture (see section 11.2.3)

52X2D1FUV-MAMAG140L & G140MPlaces the target 2±1(G140L) or 4±1(G140M) above the bottom edge of FUV-MAMA; intended for observations of very faint targets where dark current contribution should be minimized