5.11 Wavelength Settings and Ranges
The following tables show the expected wavelength ranges recorded on the detectors for each valid combination of grating and setting. Note that the FUV settings do not record the central-most wavelengths that fall into the gap between the detector segments. The nominal wavelength setting has been chosen to be the shortest wavelength that is adjacent to the gap on segment A so that the indicated wavelength is an actually recorded one.
Table 5.3: Wavelength Ranges for FUV Gratings
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Grating
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Nominal wavelength setting (Å)1
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Recorded wavelengths
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Segment B
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Segment A
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1The nominal wavelength setting has been chosen to be the shortest wavelength that is adjacent to the gap on segment A so that the indicated wavelength is an actually recorded one.
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5.11.1 "Painting" a Complete NUV Spectrum
From the table that follows (Table 5.4) an observer can plan a set of observations that best meets the needs of his or her science goals. To acquire a complete medium-resolution spectrum of an object in the NUV with COS requires 6 settings with G185M, 6 with G225M, and 8 with G285M. A full spectrum with G230L requires all four central wavelength settings. Such a complete spectrum can probably be acquired more efficiently with STIS, but COS may be more advantageous when a limited number of specific wavelengths is desired.
Table 5.4: Wavelength ranges for NUV gratings
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Grating
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Nominal wavelength setting (Å)
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Recorded wavelengths
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Stripe A
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Stripe B
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Stripe C
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1The wavelengths listed for central wavelength 2635 Å in stripe A are listed for completeness only and also in case a bright emission line falls onto the detector. Note that the NUV detector's sensitivity at these wavelengths is extremely low. To obtain a low-resolution spectrum at wavelengths below about 1700 Å we recommend G140L and the FUV channel.
2The values in shaded cells are wavelength ranges as seen in second-order light. In these cases the achieved dispersion is twice that for first-order mode.
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