|COS Instrument Handbook for Cycle 25|
G140L is a low-resolution grating (R ~ 2000) with wavelength coverage extending to 900 Å, and perhaps below. Its sensitivity at EUV wavelengths, marked in light blue in Figure 13.14, 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.
R = λ/Δλ
Figure 13.14: Wavelength Ranges for the G140L GratingTable 13.7: G140L Point-Source Sensitivity for PSA
(counts pixel-1 sec-1 pererg cm-2 sec-1 Å-1)
Figure 13.15: G140L Point-Source Sensitivity for PSA and BOAPSA × 10 is plotted to show sensitivity below 1100 Å.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 s-1 Å-1. 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.