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Checking Whether Your Data Needs to Be Recalibrated

Introduction

This page describes a quick way to determine whether there are new recommended calibration files for WFC3 data and a simple script that will allow you to update the headers of the uncalibrated data files, should you choose to recalibrate the data yourself.

Using StarView to determine the currently recommended calibration files for one or more WFC3 datasets

When WFC3 data are retrieved from MAST, the data are calibrated with a recent version of the CALWF3 and the latest calibration files. As a result of increasing knowledge about WFC3, both the software and the calibration files do change. Therefore users should check for new calibration files when they begin a serious analysis or re-analysis of the data. The simplest way to do this is to use the web-based version of StarView, which can be referenced directly from this link or from the Tools menu of the MAST home page.

StarView contains a screen called "WFC3 Best Reference Files" that can be used to find the currently recommended calibration files for all WFC3 observations. The page as indicated below has a variety of search parameters that can be used, e. g. program ID or dataset, to limit the number of records returned.

A screen shot of a portion of the results of a search on the program ID 11360, the WFC3 ERO program is shown below:

For an individual dataset or very small program, it is possible to compare a printout of the used calibration files to the currently recommended dataset by eye. However, it is more likely that you will want to export the results to a file and carry out the comparison more systematically. The results can be exported using the "Export To" button at the right hand portion of the page.

A Python script to help identify datasets for which the recommended calibration files have changed

To aid in comparing the used and currently recommended calibration files, the WFC3 team has written a simple python script that interprets an exported version of the StarView query results and compares this to values contained in the data you have on your computer. The script is written in fairly basic python, except that you must have the module pyfits installed on your machine (as will usually be the case if you have Pyraf). Simply download the script here, which for historical reasons is called upref.py, and install it in your path (or place it in the local directory containing your data files).

To use the script:

The script will print out a comparison of the used and currently recommended data files, as well as write this to a file "upref.txt". A portion of the output text file run on a now outdated version of the ERO data looks like this:

# Check best reference files for ib6w61uaq_raw.fits
       Dataset         Dataset Name                      ib6w61050                       ib6w61050 OK
       BPIXTAB     w3r_best_bpixtab        iref$u5d2012li_bpx.fits              u5d2012li_bpx.fits OK
        CCDTAB      w3r_best_ccdtab        iref$t291659mi_ccd.fits              t291659mi_ccd.fits OK
       ATODTAB     w3r_best_atodtab        iref$n9n16196i_a2d.fits              n9n16196i_a2d.fits OK
       OSCNTAB     w3r_best_oscntab        iref$q911321oi_osc.fits              q911321oi_osc.fits OK
      BIASFILE    w3r_best_biasfile        iref$u1r1346ti_bia.fits              u1r1346ti_bia.fits OK
      CRREJTAB    w3r_best_crrejtab        iref$n9i1435li_crr.fits              n9i1435li_crr.fits OK
      DARKFILE    w3r_best_darkfile        iref$u6b1348ki_drk.fits              u6b1348ki_drk.fits OK
      PFLTFILE    w3r_best_pfltfile        iref$t4t1832fi_pfl.fits              t4t1832fi_pfl.fits OK
      GRAPHTAB    w3r_best_graphtab        mtab$t2605492m_tmg.fits              u921351jm_tmg.fits X
       COMPTAB     w3r_best_comptab        mtab$u4c18498m_tmc.fits              ub31649mm_tmc.fits X
        IDCTAB      w3r_best_idctab        iref$u1r16227i_idc.fits              uab1537bi_idc.fits X
      MDRIZTAB    w3r_best_mdriztab        iref$sau1931ai_mdz.fits              ubi1853qi_mdz.fits X

and indicates that a number of the calibration files have since been updated. At this point, the observer should minimally check the WFC3 Reference File Images & Tables page to determine whether changes are likely to be minor, or decide to obtain an updated version of the data. There are two ways to do this:

Summary

Observers should be aware that as knowledge is gained about WFC3, the calibration files used to reduce the observations as part of the standard data pipeline are revised. Here we have attempted to describe a simple way to determine if there have been changes to data on your machine. We encourage users who have questions about this process or about the routine upref.py to send these questions to help@stsci.edu.


Created 01/02/2011 CP