FUV Grating G140L

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Description

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 been calibrated. The grating has three central-wavelength settings: 800, 1105, and 1280 Å.

Special Considerations

The gap between Segments A and B spans 105 Å. When settings 800 or 1105 are 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.


GratingResolving Power R = λ/ΔλDispersion (mÅ pixel−1)Plate Scale (milliarcsec pixel−1)FP-POS Step (Å step−1)
Disp. AxisCross-Disp. Axis
G140L1,500–4,00080.323.09020.1


Figure 13.14: Wavelength Ranges for the G140L Grating.

The COS sensitivity at EUV wavelengths (marked in light blue) is not known.

G140L Point-Source Sensitivity


Table 13.7: G140L Point-Source Sensitivity for PSA.

Wavelength (Å)ThroughputSensitivity (counts pixel−1 sec−1 per erg cm−2 sec−1 Å−1)Effective Area (cm2)

914

1.907e−02

1.6e+12

1.82e+03

950

2.701e−04

1.5e+12

1.75e+03

1000

2.025e−04

1.3e+12

1.49e+03

1050

4.370e−04

1.1e+12

1.14e+03

1100

3.869e−02

8.6e+11

9.00e+02

1150

2.098e−02

6.6e+11

6.70e+02

1200

3.143e−02

5.0e+11

4 97e+02

1250

3.481e−02

4.2e+11

4.01e+02

1300

3.191e−02

3.6e+11

3.34e+02

13502.642e−022.7e+112.45e+02
14002.117e−02

5.4e+12

9.58e+02
14501.726e−02

4.5e+12

7.81e+02
15001.369e−02

3.7e+12

6.19e+02
15501.052e−02

2.9e+12

4.76e+02
16008.191e−03

2.4e+12

3.71e+02
16506.315e−03

1.9e+12

2.86e+02
17005.209e−03

1.6e+12

2.36e+02
17504.523e−03

1.4e+12

2.05e+02
18003.648e−03

1.2e+12

1.65e+02
18502.789e−03

9.3e+11

1.26e+02
19001.829e−03

6.3e+11

8.27e+01
19501.012e−03

3.6e+11

4.58e+01
20003.978e−04

1.4e+11

1.80e+01
20501.308e−04

4.9e+10

5.92e+00
21004.006e−05

1.5e+10

1.81e+00
21485.357e−06

2.1e+09

2.42e−01


Figure 13.15: G140L Point-Source Sensitivity for PSA and BOA.

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

G140L Signal-to-Noise Ratio


Figure 13.16: 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 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.

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