INTRODUCTION

Archive research, data mining and VO, are becoming powerful tools in doing science; but, scientific data integrity has to be "guaranteed" before massive research projects are started.

Typically there are fewer resources available for work on legacy instruments than for operational instruments. Post Operational Archives (POA) work falls under the project agreement between ESA and NASA for legacy instruments. We investigated the feasibility of improving the FOS data archive by resolving issues with the STSDAS offline FOS calibration pipeline (using physical models).

In August 2001, the POA project team released v1.2 of the STPOA IRAF external package. It contains the final version of the replacement FOS calibration pipeline called `poa_calfos'.

STPOA V1.2 RELEASE

The STPOA external IRAF package can be downloaded from:

ftp.eso.org (/pub/stpoa)

The STPOA package can be installed at any IRAF user location. The August 2001 v1.2 release is in place at ESO and STScI. It contains four tasks:

poa_calfos - Post Operational Archive calibration pipeline for FOS.
poa_preproc_fos - Task for pre-processing FOS data, for poa_calfos pipeline.
poa_procfos_all - Task that runs poa_preproc_fos and poa_calfos back-to-back.
pfos_pix2wav - Task to calculate λ positions from FOS pixel positions.

(`pfos_pix2wav' has been updated to include the subpixel POA correction to the data; hence it is now posible to gain the benfits of "oversampling" without the drawbacks of resizing the data themselves.)

POA FOS solution is available for the following FOS datasets (POA criteria):

Detector: BLUE
Grndmode: SPECTROSCOPY, RAPID-READOUT, IMAGE
Fgwa_id: H13, H19, H27, H40, H57, L15, L65
Aper_id: A-1, A-2, A-3, A-4, B-1, B-2, B-3, B-4

POA FOS data all-processor task (poa_procfos_all) checks to see if the data fall within the POA processing criteria:

- If yes, it runs the `poa_preproc_fos' task to update header reference file information and then runs the pipeline `poa_calfos'.

- If no, it executes `calfos' instead of running the POA correction

Calibration reference files are internal to the STPOA software; there is a parameter switch to use external STScI CDBS versions of these reference files once they are embedded into the system.

The POA project team has officially taken over the support for the FOS. Our website contains the most up to date documentation, technical information and software for the FOS:

http://www.stecf.org/poa/FOS/index.html

The FOS helpdesk for science, technical and software issues is:

stdesk@eso.org

HST FOS ARCHIVE

ST-ECF and CADC HST archives support FOS on-the-fly (OTF) calibration using the new pipeline:

http://www.archive.eso.org (HST Science Archive)

The user can search and retrieve FOS dataset(s) in either archive; the default OTF re-calibration is done using the POA pipeline unless the data do not fit the POA criteria (then, `calfos' is run instead):

STScI HST archive will be updated by the end of 2001 with all FOS data re-calibrated (RED, BLUE, raw and output). Those data that do not have a POA correction, will be re-processed with `calfos'.

The results of the POA work on the FOS create a homogeneous archive for this HST instrument. A researcher can view the FOS data from `90 to `97 together in a coherent manner. They will also have more confidence that the data they are using has been substancially improved upon.

SOFTWARE IMPROVEMENTS

The new software fixes the following problems for ~90% of the FOS BLUE science data:

The residual effects from the Geomagnetic Image Motion Problem (GIMP)
The offsets introduced by the electronic setup of the detector (YBASE)
The variations of the ambient temperature in the FOS optical bench
The dispersion relations have been substantially improved for all the gratings
The flat fields have been recalculated using the POA correction
The darks have been rescaled using a physical model

Wavelength Uncertainties issue...

Uncertainty in the wavelength zeropoint is reduced from as much as 5 pixel to less than one pixel. Comparing the results of the wavelength offsets from the zeropoint, using the old pipeline `calfos' (open symbols) and the new pipeline `poa-calfos' (closed symbols):

Dispersion Relations issue...

Previous dispersion relations were based on 3rd order polynomials to describe each grating separately; the solution was based on an inaccurate list of (PtCr-Ne lamp) lines, and the most important blue grating (G130H) was never properly calibrated due to scattered light problems. `Calfos' dispersion solution residuals are shown on the left (above), and the `poa_calfos' solutions are on the right. The POA solution is based on a physical model of the aperture-diode array optical path, uses the same set of parameters to describe all the gratings, and uses an improved lamp line list from NIST.

Flat field reference files were re-processed using the POA correction. Flats re-creation process was ported from VAX IDL to an automated script-driven setup on UNIX/Solaris.

Darks are being scaled to a new parameter called L-shell, which is based on a model of the background using geomagnetic latitude/longitude. It reflects the dark current better than the previous parameters and it fits the calibration data better over the lifetime of the FOS.

CONCLUSIONS AND A LOOK AHEAD

The FOS section of the HST Handbook, FOS ISR's and POA technical reports will be written and/or updated in fall 2002 with the details of the POA corrections.

POA Publicity!! All FOS PI's have been sent a letter which advertises our work. We also published and sent out an article, which details the STPOA v1.2 final release, in the ST-ECF 29th Newsletter (July 2001).

POA work starts to ensure VO validation and credibility - this is a MUST for future archives in order to ensure scientific integrity.

We will use our expertise from FOS and apply them to the next POA project - Space Telescope Imaging Spectrograph (STIS); this project will start in early 2002.

The lessons learned from POA work should be applied in designing archives and software for future instruments.

Go to documentation and download pages.