E.15 The Cycle 28 Calibration Plan

The Cycle 28 calibration plan was executed from November 2020 through October 2021. The individual programs are listed in Table E.16 and are described in more detail on the WFC3 Calibration Plan webpage. Following the link to Cycle 28 Calibration, a similar table may be found with direct links to the phase II programs and observation dates. This information may alternately be accessed via the HST Program Information webpage by entering the Proposal ID.

The WFC3 Cycle 28 section also links to a PDF presentation summarizing WFC3 and comparing the Cycle 28 plan with the prior cycle. This document contains more details on the calibration justification and in many cases includes supporting figures with the latest results from regular monitoring.

The Cycle 28 calibration plan was designed to:

• Maintain and update the standard reference files (biases, darks, linearity, CTE traps, UVIS anomalous QE pixels, post-flash)
• Monitor the health of the instrument (throughput, gain, hysteresis, bad/hot pixels, sink pixels, CTE decline, stability of the post-flash LED, filter transmission, state of the CSM, number of IR blobs, wavelength and flux stability of the grisms)
• Support new initiatives and obtain supplemental (non-routine) calibration data

In this cycle, the IR Grism Flux Monitor (program 16408) has been modified to:

• Quantify sensitivity losses in the IR grisms by supplementing the annual GD153 data with two additional WD standards

Five new calibration programs will supplement the standard monitoring. These programs (16439, 16440, 16441, 16512, 16518) were designed to:

• Check whether IR filters are losing sensitivity similar to the grisms by repeating prior scanned observations of M35 

• Recheck the optimal background (post-flash) level, as CTE losses continue to grow

• Measure the impact of CTE on very faint stars

• Test for changes in the F110W sensitivity with time by leveraging off of prior observations of the M4 cluster.

• Check the UVIS focus cross-calibration from F410M to F606W for 'despace' values below 2 microns.

The results of these calibration programs will be documented in Instrument Science Reports on the WFC3 website at:
http://www.stsci.edu/hst/instrumentation/wfc3/documentation/instrument-science-reports-isrs

Table E.16: The Cycle 28 Calibration Programs