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Observation Overheads

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The ITC includes the following observation overheads: acquisitions (possibly more than one for long observations), detector readout, telescope offsetting, and re-centering of spectroscopic observations when required. These overheads are calculated for all instruments and modes except for GSAOI. These calculations make several assumptions about the observing strategy which may not apply to your program, so please review the results carefully.

Setup / Acquisition overheads are instrument and mode specific:

The ITC assumes one full acquisition for every 2 hours of science (where the 2 hours includes offsetting, readout, and DHS overheads, but excludes time for re-centering).

The ITC assumes one re-centering for these spectroscopic visits longer than 1 hour:

  • Slit spectroscopy guided with PWFS
  • GMOS IFU spectroscopy guided with PWFS where the S/N is <5 per exposure
  • NIFS spectroscopy where the S/N is <5 per exposure

Offsetting overheads are based on the offset distance specified in the "Dither offset size" field of the ITC form. Slit spectroscopy assumes an ABBA offset pattern, while imaging and IFU spectroscopy assumes an ABAB offset pattern. Set the offset size to zero to if you are not planning on offsetting and these overheads will be excluded.

The ITC does NOT include overheads for partner calibrations like flats, arcs, or standard stars.

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