E.14 The Cycle 27 Calibration Plan

The Cycle 27 calibration plan was executed from November 2019 through October 2020. The individual programs are listed in Table E.15 and are described in more detail on the WFC3 Calibration Plan webpage. Following the link to Cycle 27 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 27 section also links to a PDF presentation summarizing WFC3 usage and comparing the Cycle 27 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 27 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, two standard monitoring programs have been restructured from Cycle 26. These programs (16021, 16030) were designed to:

• Quantify losses in the UVIS sensitivity using spatial scans (previously called ‘UVIS Contamination Monitor')
• Monitor the ‘UVIS and IR Photometric Calibration’ via staring mode observations of HST standards

Five new calibration programs will supplement the standard monitoring. These programs (16020, 16022, 16023, 16029, 16031) were designed to:

• Measure the stability of the tungsten lamp output immediately after turn-on
• Refine the UVIS grism wavelength calibration across the entire detector with better 2D sampling
• Finalize the flux calibration of the UVIS grism with similar spatial sampling as for the wavelength calibration
• Recheck the optimal UVIS background level to mitigate CTE losses
• Check for time dependent sensitivity in the IR detector grisms and filters

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.15: The Cycle 27 Calibration Programs