Space Telescope Science Institute
COS Instrument Handbook
help@stsci.edu
Table of Contents Previous Next Index Print


Cosmic Origins SpectrographInstrument Handbookfor Cycle 22 > Chapter 13: Spectroscopic Reference Material > FUV Grating G140L

FUV Grating G140L
Description
G140L is a low-resolution grating (R ~ 2000) with wavelength coverage extending to 900 , 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 .
Special Considerations
The gap between segments A and B spans 105 . 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 may be contaminated by second-order light.
Resolving
Power
R = λ/Δλ
Dispersion
(m pixel–1)
FP-POS
Step
( step-1)
Figure 13.14: Wavelength Ranges for the G140L Grating
The COS sensitivity at EUV wavelengths (marked in light blue) is not yet known.
G140L Point-Source Sensitivity
Table 13.7: G140L Point-Source Sensitivity for PSA
Sensitivity
(counts pixel-1 sec-1 per
erg cm-2 sec-1 -1)
Figure 13.15: G140L Point-Source Sensitivity for PSA and BOA
PSA 10 is plotted to show sensitivity below 1100 .
G140L Signal-to-Noise Ratio
Figure 13.16: Point-Source Signal-to-Noise as a Function of STMAG for G140L
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 -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.

Cosmic Origins SpectrographInstrument Handbookfor Cycle 22 > Chapter 13: Spectroscopic Reference Material > FUV Grating G140L

Table of Contents Previous Next Index Print