|WFC3 Instrument Handbook for Cycle 25|
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
5. Optional Parameters: the 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 Requirements: see 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).