Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

5.8 EXTENDED

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Optional Parameter EXTENDED (NO (the default), or YES) populates a science header keyword with this information to inform the calcos pipeline that the target is an extended source. The keyword may be used to activate special data reduction procedures. No aspect of on-board data-taking is affected by this parameter.

As noted several times in this document, COS is designed as a point-source spectrograph. Observing extended objects with COS will, at best, produce a spectrum with significant degradation in spectral resolution. For the NUV, the situation is much worse because a source that fully fills the COS aperture will lead to cross-contamination among the three spectrum stripes on the MAMA detector.