The Ly- detector has a window (short-wavelength cutoff at 1130 ) and a KBr photocathode. At the null position of the grating the Ly- spectral line ( 1216 ) is centered on the detector. The nominal wavelength range on the detector is 1145 to 1287 . With grating motions the wavelength range can be extended down to 1070 (detection limited by window transmission) and up to 1361 . The dispersion is 5.54 /mm, or 0.1385 per pixel (total width 141.8 ). The following solar lines fall in the nominal wavelength range: H I 1216, Fe XII 1242, N V 1238, Si III 1206.
The dispersion of the O VI channel is 3.70 /mm or 0.0925 per pixel in first order, and 1.85 /mm or 0.0463 per pixel in second order. The null position of the grating is such that O VI 1032 is near the center of the O VI detector. The primary purpose of the O VI detector is to observe O VI 1032/1037 in first order. It is also used to observe Si XII 499/521 in second order. The wavelength range for this detector is 984 to 1080 ( i.e., 492 to 540 in second order). Grating motions can extend this range down to 937 and up to 1126 ( i.e., 469 to 563 in second order). The following solar lines fall within the full range: O VI 1032/1037, C III 977 and He II 1085 (first order), Si XII 499/521 (second order). The O VI channel also includes a convex mirror which focusses the Ly- radiation onto the O VI detector. This provides a redundant capability to measure the Ly- profile, and also allows observations of Mg X 610/625 in second order. The nominal wavelength range for the redundant Ly response is 1220 to 1124 (610 to 562 second order). Grating motions extend this range from 1268 to 1076 (634 to 536 second order).
The spectral resolution of the Ly- and O VI channels will be adequate to resolve the profiles of the Lyman lines, but it might, depending on the line widths, be marginal for the lines of heavier ions in the standard mode. Therefore, it might be necessary to obtain several exposures at different grating positions to measure the profiles of heavier ions.