|COS Instrument Handbook for Cycle 25|
As shown in Figure 6.3, the COS NUV channel is sensitive to wavelengths above 3200 Å, an important consideration when imaging red objects. For stars with effective temperatures above 6000 K, the effect is negligible, but it grows to about 20% at 5000 K, and below 5000 K it quickly becomes large.If you upload a spectrum into the ETC to calculate exposure time of an imaging exposure, whether for a target acquisition or a scientific observation, be sure that the spectrum spans the full range of wavelengths to which the NUV channel is sensitive, from about 1600 Å to 12,000 Å. Failure to do so can produce a misleading result.The COS ETC expects input spectra to extend out to 12,000 Å and will return a warning message (“Partial overlap between instrument throughput band and input spectrum”) if they do not. This message indicates that the ETC may return incorrect results due to the incomplete source spectrum. Users should take care to be sure that the input source spectrum covers the entire wavelength range of the detector, accounting for any impact to the spectral coverage due to the redshift of the source.