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Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 14

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F25SRF2-NUV-MAMA, Longpass

Description

The F25SRF2 filter with the NUV-MAMA provides high-throughput broad-band near-UV imaging with better rejection of geocoronal emission than the F25MAMA but worse than or F25QTZ modes. It provides the same field of view and high spatial resolution.

Recommended Uses

This filter has slightly higher throughput than F25QTZ, but lets in geocoronal [O I] 1302 + 1306 Å. In most cases the sky background will still be lower than the detector background.

Special Considerations

Sky background on the day side of the orbit contains a significant contributions from [OII] air glow emission at 2471 Å and [O I] air glow at 1302 + 1306 Å. In high-background conditions, the sky background can dominate the detector background. In average day-side observing conditions about half the background will be from the sky and half from detector dark current. Also, the background through F25SRF2 will be about 10% higher than through F25QTZ. Observers can limit the background by using the DARKTIME special requirement.

Users should also consider whether the ACS HRC with the F220W or the F250W filter might be a better choice for their science goals.

Pivot (Å) FWHM (Å)
AB mag zeropoint
Speak
B
R80 (arcsec) Flux in central pixel
2299.3
1127.7
23.915
1.59e+14
1126.5
0.32
8%

Figure 14.41: F25SRF2 NUV-MAMA Integrated System Throughput and Redleak


 

Table 14.17: Throughput and Sensitivity for F25SRF2 NUV-MAMA
l
Sensitivity
Throughput %
1300.
1.23E13
0.42
1400.
2.83E13
0.89
1500.
3.27E13
0.96
1600.
3.25E13
0.89
1700.
3.32E13
0.86
1800.
4.01E13
0.98
1900.
5.64E13
1.30
2000.
8.32E13
1.83
2100.
1.11E14
2.32
2200.
1.33E14
2.64
2300.
1.47E14
2.80
2400.
1.56E14
2.84
2500.
1.58E14
2.78
2600.
1.57E14
2.66
2700.
1.53E14
2.49
2800.
1.46E14
2.28
2900.
1.21E14
1.83
3000.
9.26E13
1.36
3100.
4.58E13
0.65
3200.
2.04E13
0.28

Figure 14.42: Point Source S/N vs. V+AB for the F25SRF2 NUV-MAMA mode. Top curves are for DARKTIME. Bottom curves are for average sky. Curves are labeled by required exposure time (sec).


 
Figure 14.43: Extended Source S/N vs. V+AB for the F25SRF2 NUV-MAMA mode. Top curves are for an area of 0.2 arcsec2; bottom curves are for 1 arcsec2. Average sky assumed. Curves are labeled by required exposure time (sec).


 
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