FOS: FOS Advisories

ST-ECF, POA

FOS Advisories

New POA_CALFOS pipeline available as part of ST-POA package release.:

POA_CALFOS replaces CALFOS as the standard IRAF STSDAS FOS calibration package offering an improved correction to the zero point offsets found during the post-operational analysis of the contributing errors for BLUE data sets.

FOS Paper Products Now Support Polarimetry.

The paper product task pp_dads has been enhanced to support creation of spectropolarimetry paper products. The upgrade was part of the STSDAS release 2.0.2. The task produces the standard plot of flux (and log(flux)) versus wavelength, as well as plots of Q/I and U/I (with one-sigma statistical error bars) versus wavelength (in 32 bins of 64 pixels each).

The task does not (as yet) update the Calibration Status paper product Summary page, which is intended to include a listing of all reference files used in calibration, to include mention of the post-COSTAR polarimetry correction reference file.

FOS/BL Wavelength Quick-FIX cl script available.

FOS Spectropolarimetry Closeout Documentation available.

FOS Closeout Calibration Sensitivity reference files available.

An updated set of AIS sensitivity reference files and tables has been delivered. The new calibration derives from the FOS Closeout Calibration analysis.

POST-COSTAR: The new files incorporate the results of standard star observations taken over the entire post-COSTAR period (as opposed to the 1994-95 period covered in the previous calibration set). Additionally, all standard star observations have been flatfield corrected with the FOS Closeout Flatfields appropriate to each individual observing epoch. Time-dependent sensitivity changes continue to be tracked for FOS/RD G190H and G160L only. Aperture-throughputs for 0.1-PAIR and the barred apertures have now been incorporated so that these apertures can be flux-calibrated by normal running of CALFOS.
PRE-COSTAR: As for the post-COSTAR case, aperture-throughputs for 0.1-PAIR and the barred apertures have been incorporated so that these apertures can be flux-calibrated by normal running of CALFOS. No changes to the pre-COSTAR sensitivities have been introduced, however.

The FOS chapters in Volume II of the third edition of the HST Data Handbook provide a complete discussion of the limitations of FOS flux calibration with these reference files. A full description of the new calibration will be presented in forthcoming FOS ISR CAL/FOS-157.

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

ftp.stsci.edu/cdbs/yref

FOS Closeout Calibration Flatfield reference files available.

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/yref

Possible misleading reports on FOS STARVIEW screens.

The STARVIEW screen which reports a comparison of the `Used' vs latest `Recommended' Calibrations available for any given FOS dataset is misleading in certain cases. When reporting on a dataset which was archived before the Average Inverse Sensitivity (AIS) flux calibration method was available this tool correctly reports that none of the associated calibration files were `used' and also correctly lists the files needed to perform this calibration. However, the STARVIEW screen incorrectly qualifies the `Level of Change' of these calibrations as `N/A'. The AIS corrections are ALWAYS RECOMMENDED. This notice applies as well to data archived before implementation of the default Scattered Light Correction (.cy9 reference file).

Improved algorithm for accumulator "wrap-around" correction.

The 16-bit FOS accumulators were limited to 65536 counts in any individual read out before they would "wrap around". The following IDL code (fos_overflow.pro) presents an improved algorithm for removing detector "wrap-around" from FOS observations. This code has not been incorporated into STSDAS. It is provided here on an "as-is" basis as an algorithm that has been used by members or the FOS team to "unwrap" some special cases which were not handled successfully by the STSDAS unwrap algorithm. Thorough testing of the code to insure complete backward compatibility with the STSDAS unwrap algorithm has not been performed. Although the fos_overflow.pro algorithm has not failed in any application to date, no warranty, express or implied, is provided.

IDL SOURCE CODE: (ASCII text)

ISR-148, Observed FOS PSFs and LSFs, has been withdrawn.

(9Dec97) The post-COSTAR, FOS/RED, observed PSF provided in CAL/FOS ISR-148 includes artifacts. The image was created by co-addition of 30 separate data sets. Several of these data sets have been found to contain possible reflection and diffraction effects due to the target's proximity to the edge of the aperture. Therefore the FOS/RED PSF, in particular, should not be used.

FOS Sensitivity Below 1200A: Methods of Analysis.

ABSTRACT: (30 January 1998) We wish to remind observers that FOS instrumental sensitivity is a very steep function of wavelength shortward of 1200 Anstroms. Although instrumental sensitivity is determined to 3% accuracy in this region, this steep sensitivity gradient requires accurate knowledge of observed wavelengths to insure accurate flux calibration. Common instrumental uncertainties can produce important systematic errors in pipeline processing. See the full text of this advisory.

FOS Advisories Archives

Text listing of older advisories and summaries provided to FOS observers and archival researchers.