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.
MAST Processing Status Page
Click here to view HST data reprocessing activities from the Mikulski Archive for Space Telescopes (MAST)
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 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, 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:
- Export the results of a query on the StarView Best Reference File page in comma-separated (CSV) format to the directory containing your data. An example of this file for the query above is here.
- Next run the script on your data, e.g.
upref.py table.csv *raw.fits
where table.csv is the name of the CSV file exported for StarView and the remaining arguments are one or more uncalibrated fits files.
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:
- One can re-retrieve the data from MAST
- One can re-calibrate the data at the observer's home institution. Procedures for recalibrating the data are described in the WFC3 Data Handbook. To aid in this recalibration, upref.py also produces a file called upref.cl that contains a series of 'hedit' commands that can be run from IRAF
cl <upref.cl
- which will update the headers in the raw data files.
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.