FUV Grating G140L

Description

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.

Special Considerations

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.

Grating	Resolving Power R = λ/Δλ	Dispersion (mÅ pixel–1)	Plate Scale (milliarcsec pixel-1)		FP-POS Step (Å step-1)
			Disp. Axis	Cross-Disp. Axis
G140L	1,500 - 4,000	80.3	23.0	90	19.6

Figure 13.13: 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

Wavelength (Å)	Throughput	Sensitivity (counts pixel-1 sec-1 per erg cm-2 sec-1 Å-1)	Effective Area (cm2)
950	1.565E-04	2.7E+10	7.08E+00
1000	1.338E-04	2.4E+10	6.05E+00
1100	5.054E-03	1.0E+12	2.29E+02
1200	2.987E-02	6.5E+12	1.35E+03
1300	3.319E-02	7.8E+12	1.50E+03
1400	2.286E-02	5.8E+12	1.03E+03
1500	1.497E-02	4.1E+12	6.77E+02
1600	8.962E-03	2.6E+12	4.05E+02
1700	6.026E-03	1.9E+12	2.73E+02
1800	3.932E-03	1.3E+12	1.78E+02
1900	2.046E-03	7.0E+11	9.26E+01
2000	4.337E-04	1.6E+11	1.96E+01
2100	2.886E-05	1.1E+10	1.31E+00

Figure 13.14: G140L Point-Source Sensitivity for PSA and BOA

PSA × 10 is plotted to show sensitivity below 1100 Å.

G140L Signal-to-Noise Ratio

Figure 13.15: 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 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.