6.2 Specifying a UVIS Observation

Using the Astronomer’s Proposal Tool (APT), it is relatively simple to specify the parameters for a UVIS observation. Detailed documentation of the specifications can be found in the Phase II Proposal Instructions. The parameters available to General Observers for the UVIS channel are the following:

  1. Configuration: always WFC3/UVIS
  2. Mode: always ACCUM
  3. Aperturemust be specified; see Section 6.4.4 and Section 6.4.5 for the dimensions, location, and reference point (target placement) of the full array and subarray apertures.
  4. Spectral Elementmust be specified for each exposure; see Section 6.5
  5. Optional Parametersthe options include FLASH (to post-flash a specified number of electrons to reduce CTE losses; Section 6.9.2), CR-SPLIT (to split an exposure into a specified number of subexposures for cosmic ray rejection - but note that CR rejection can also be accomplished by combining dithered exposures; Section 6.11.2), BIN (to perform on-chip binning by a specified number - but beware that this increases the area affected by bad pixels and cosmic rays; Section 6.4.4), BLADE (to make short exposures with less vibration by selecting shutter blade A; requires approval - see Section 6.11.4), and INJECT (to implement charge injection to reduce CTE losses - but the use of this option is not generally permitted for science observations; see Section 6.9.2).
  6. Special Requirementssee the Phase II Proposal Instructions for details of Special Requirements related to the timing of visits and for dithering and mosaicking. Also available is the exposure-level Special Requirement POS TARG for offsetting the target from the default reference point of the aperture (see Section 6.4.3 for a discussion of the UVIS channel coordinate systems, Section 6.4.5 for reference points, and Appendix C for the POS TARGs associated with the WFC3 patterns).
  7. Number of Iterations and Time per Exposurethe exposure time for the UVIS channel must be an integer multiple of 0.1 s, ranging from 0.5 to 3600 s, except that 0.6 s is not allowed; see Section 6.7.1 for details).