1.1 New for Cycle 28

We have made the following updates to the WFC3 Instrument Handbook for this cycle:

  • We discuss recent results from studies of count rate non-linearity on the WFC3/IR detector (Section 5.7.6).
  • We discuss the construction of focus-diverse PSF models for five commonly used UVIS broad-band filters and their relationship to HST focus (Section 6.6.4).
  • We have extensively updated the description of photometric calibration (Section 6.10).
  • We point out the existence of an offset between spatial scan images made in forward and reverse modes (Section 6.12.3).
  • We update advice to observers using the spatial scan mode and demonstrate the advantage of monitoring UVIS system throughput with spatial scan data (Section 6.12.3).
  • We state the increased drift rate associated with using a single guide star (Section 6.12.4, Section 7.10.4).
  • We summarize the results of recent studies of persistence on the WFC3/IR detector and advise the use of dither steps greater than 10 pixels for some photometric programs (Section 7.9.4).
  • We note that the solar exclusion angle for HST observations has increased from 50 degrees to 55 degrees (Section 7.9.5, Section 9.7.1).
  • We provide new references to studies of the "blobs" in WFC3/IR images and discuss the date-dependent bad pixel tables that track the appearance of blobs (Section 7.9.6).
  • We discuss the impending release of tools and a Jupyter notebook to assist users of the DASH mode to calibrate their observations (Section 7.10.6).
  • We provide a more detailed discussion of the background in WFC3/IR grism exposures and illustrate the three components of the background (zodiacal light, He I airglow emission, and scattered light) in G102 and G141 images (Section 8.5).
  • We confirm the stability of the geometric distortion solution for the WFC3/UVIS F606W filter and summarize the delivery of IDCTAB reference files for the WFC3/IR detector and the WFC3/UVIS detector (Appendix B).
  • We have added a summary of the WFC3 calibration plan for the upcoming cycle in Appendix E