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I just got my ACS data. What are all these files?

I just got my ACS data. What are all these files? How can I quickly display my science data?

If you are unfamiliar with ACS file formats and naming conventions, it can be a bit confusing at first to sort out which files you really need, which you might be able to delete, and how to begin working with your ACS data.

The following files are the most critical, but depending on your data reduction plans (see below), you probably only need a subset of them:

*_asn.fits (association tables; relate CR-SPLIT or dithered data)
*_raw.fits (raw images used to generate all of the following)
*_flt.fits (flat-fielded images; multidrizzle input)
*_crj.fits (cosmic-ray cleaned/combined images; PyDrizzle input)
*_drz.fits (distortion corrected PyDrizzle output in e/sec)
Note that the science data (sci), data quality (dq), and error (err) arrays are stored in FITS extensions within these files. The drizzled files (*drz.fits) include weight (wht) and context (ctx) extensions. In IRAF, use tprint to see the contents of association tables, and catfits to see all the FITS extensions. To quickly examine your files, and display the science array in any of the images above:
cl> tprint *asn.fits
cl> catfits *_drz.fits
cl> display *_drz.fits[sci,1] zr+ zs+
These files may or may not be immediately (or ever) useful to you:
*_sfl.fits (calibrated REPEAT-OBS combined image)
*_trl.fits (CALACS trailer file; logs each step)
*_spt.fits (telemetry and engineering data)
Your calibration reference files may also be present, if you requested them. The "best" reference files are typically available 2-3 weeks after your observation date, e.g. the dark reference file (for your particular observation date) takes some time to produce.

If you plan to recalibrate your data (re-run CALACS), you only need the raw files (*raw.fits), the best reference files, and the association tables (*asn.fits) that CALACS needs as input. Alternately, you could just wait 2-3 weeks after your observation date (until the best reference files are in place in the calibration pipeline), and then re-request your data via on-the-fly-reprocessing (OTFR). If you plan to re-run PyDrizzle, the cosmic-ray cleaned images (*crj.fits) will be needed as input.

If want to run multidrizzle, you will need the flat-fielded images (*flt.fits) as input. If they don't already exist, you will need to set EXPSCORR=PERFORM in your raw image headers and re-run CALACS to generate them.