G140L is a low-resolution grating (R
~ 2,000) with wavelength coverage extending to 900 Å. and perhaps below. Its sensitivity at EUV wavelengths, marked in light blue in Figure 13.13
, has not yet been calibrated. The grating has two central-wavelength settings, 1105 and 1280 Å.
The gap between segments A and B spans 105 Å. To fill this gap requires exposures at both
central-wavelength settings. When setting 1105 is used, the high voltage on Segment B must be lowered to avoid a dangerously high count rate from zero-order light. Wavelengths longer than 2150 Å may be contaminated by second-order light.
The top axis displays constant Fλ
values corresponding to the STMAG units (V+STMAGλ
) on the bottom axis. Recall that STMAG = 0 is equivalent to Fλ
= 3.63E-9 erg cm-2
. Colors refer to exposure times in seconds. The edge of the shaded area corresponds to the bright-object screening limit. Use of the PSA is assumed.