FOS Closeout Calibration:

FOS Closeout Calibration: Flatfield Reference File Update and Delivery (30-Jan-1998)

Revised post-COSTAR FOS flatfield reference files for SINGLE apertures have been delivered. The new files derive from the FOS Closeout Calibration analysis and should be used for all post-COSTAR calibration. No new pre-COSTAR flatfields are available at this time.

SINGLE apertures: The new files incorporate the results of standard star observations taken over the entire post-COSTAR period (as opposed to the 1994 period covered in the previous calibration set). Photocathode granularity variations are tracked to the full extent of available data. Significant improvement in both the quality of the flatfields and time-dependent correction is available, especially for FOS/RD G190H, G270H, G400H, and FOS/BL G130H and G270H.
Paired apertures: New flatfields have been developed for paired apertures, as well. These files are in the final stages of formal delivery verification and will be announced shortly. The paired aperture set does not include as many epochs of observation as for the more commonly used SINGLE apertures, but flatfields appropriate to all paried aperture exposures (except the very small number of 0.1-PAIR exposures obtained with gratings other than FOS/RD G570H) will be available.

The FOS chapters in Volume II of the third edition of the HST Data Handbook provide a complete discussion of the limitations of FOS flatfielding and include the results based upon these reference files. A full description of the new calibration will be presented in forthcoming FOS ISR CAL/FOS-158.

The accompanying table lists the best set of FOS flatfield reference files. All of these files are available through StarView or via anonymous ftp from

ftp.stsci.edu/cdbs/cdbs2/yref

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30 January 1998