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What To Do When You Get an Exception Report for WFC3

If something may have gone wrong with your WFC3 observations, you will get an email containing an HST exception report detailing which of your Exposure IDs were affected. It asks you to download your data from MAST, determine whether the S/N and/or flux of your data reached the expected levels, and determine from a quick-look inspection whether your data appear anomalous in any other way. Here we provide a checklist with more detailed steps on inspecting WFC3 data for potential problems, and a Python Jupyter Notebook that will guide you through each of the following steps. 

If at the end of these steps, you find a problem in your data, file a Hubble Observation Problem Report (HOPR) within 90 days of the date that data were delivered. When filing a HOPR you must include all relevant information about the observing issue and justification as to why you are requesting a repeat observation. That information can be obtained from the steps below. If after these steps you are unsure whether your data have an issue, contact the Help Desk.

  1. Download your data. This will include the FLT files as well as the observing logs (JIF) and jitter files (JIT). If your data are from the IR detector, please also download the Intermediate MultiAccum files (IMA), which allow you to see each individual read. 
  2. Display your data. In the Jupyter Notebook, we utilize display_image, a custom Python function that displays the science, error, and data quality arrays of any WFC3 image. While viewing your data and assessing the quality, please keep in mind that the UVIS and IR detectors both have their own unique anomalies. For a full list of all known WFC3 anomalies please see WFC3 ISR 2017-22. Additionally, there is a dedicated WFC3 Anomalies webpage.
  3. Review the headers of the observing logs (JIF files) for problems. JIF files contain useful information including: Pointing Control System data, World Coordinate System parameters, and spacecraft data taken during the observations. The "Problem Flags and Warnings" section of the headers of extensions 1+ will be populated if problems exist. There may be problems with guide star acquisitions (T_GSFAIL), or telescope slewing (T_SLEWING), among others. The GUIDEACT header keyword in the headers of extensions 1+ lists the actual guiding mode for each exposure, which allow you to determine if the intended guiding mode was acquired.
  4. Plot the data in the jitter file (JIT). The jitter files are FITS tables that provide various observatory and science instrument statistics throughout a given exposure. Columns from the jitter table that can help determine if a problem occurred include: SI_V2_AVG and SI_V3_AVG (the mean jitter in V2/V3 over 3 seconds) as well as SI_V2_RMS and SI_V3_RMS (the RMS jitter in V2/V3 over 3 seconds). A description of each column as well as the corresponding unit can be found in the headers of the JIT file.
  5. Further analysis: Determine whether the signal-to-noise and/or flux of your data reached the expected levels, and check any point spread functions or sources that appear in your exposures for signs of drifting. We recommend using the Astropy packages, photutils and imexam, to accomplish these steps. In the Jupyter Notebook, we show an example of detecting sources and making radial profile plots. 

If you wish to repeat the observations, please submit a HOPR within three months (90 days) of the date that the data were delivered, following the instructions provided in the email. As always, please contact the Help Desk if you have any questions or concerns.

Last Updated: 06/13/2024


HST Help Desk 

Please contact the HST Help Desk with any questions.