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Hubble Space Telescope
WFPC2 Header Changes due to OPUS 10.0 Update

by Daryl Swade

OPUS 10.0 includes a major change for the WFPC2 and FOC science data processing pipelines in OPUS. In response to the diminishing support for the VMS/VAX platform, both within STScI and by third-party software, these OPUS pipelines were ported to the ALPHA/VMS platform.

The output of Generic Conversion will be FITS format with image extension. Currenly, the data products are converted from FITS to GEIS in the OPUS pipeline before calibration is executed. The output of calibration will still be GEIS format. Future plans will move this conversion process after calibration.

Here is a summary of the header changes.

All headers:

- FITS standard TELESCOP keyword is added to all headers. The value of this keyword is always defaulted to 'HST'.

TELESCOP= 'HST            ' / telescope used to acquire data

- The precesion of a number of keyword values has changed. These keyword values are derived from the telemetry and undergo a unit conversion in OPUS. The floating point representation change between VAX and ALPHA compilers can account for this change that does not occur in any significant digit.

- The header positions of the DATE, FILETYPE, INSTRUME, and EQUINOX keywords have changed.

D0H:

- STDCFFP keyword is now populated correctly with the value of the DCF fill pattern '0x5569'.

- For internal observations only, the default values for the ORIENTAT and CRPIXn keywords has changed for WFPC2 and FOC to the STIS/NICMOS defaults. These keywords have no relevance for internal observations. ORIENTAT default changes from value of previous observation to 0.0. CRPIXn default changes from 1 to reference pixel position.

SHH:

- UTCO1 keyword value has changed because of redefinition of the leading bit of the s/c clock time to accommodate the s/c clock roll-over. UTCO1 is now unsigned 32 bit integer instead of signed 32 bit interger. This may cause some problems with any FITS readers that uses this keyword. Note that the important keyword, UTC0, has not changed. UTC0 is the MJD representation of the bits in the UTCO1 and UTCO2 keywords.

UTCO1   =   bytes 5-8 of UTC0                               I4 
UTCO2   =   bytes 1-4 of UTC0                               I4 
UTC0    =   Coordinated Universal Time (Mod Julian Date)    R8  

- A number of keyword values have changed, but retain the same meaning. This is because WFPC2 and FOC now share common code with STIS and NICMOS for setting the values of these keywords:

TRK_TYPE is now 'F' instead of 'NO'.
PAR_CORR is now 'Y/N' instead of 'T/F'.
CALIBRAT is now 'T/F' instead of 'Y/N'.

In the latter two cases, the OPUS code still interprets the keyword value correctly. However, values in the archive catalog for WFPC2 and FOC will be mixed.

Track48 or track52 commanding have never been, and never will be, implemented. TRK_TYPE can never have anything but a negative value, and this keyword along with T51_RATE and T51_ANGL should be removed from the shh/spt headers.

- 33 keywords have been added to the end of the shh/spt header for all current and future instruments. These keywords provide definitions of aperture parameters in several different coordinate systems and conversion information to move between these coordinate systems. They are directly filled from aperture relations in the PDB. These new keywords are necessary now because the OPUS-IRAF interactive target acquisition software has been rewritten for use by ALPHA/VMS and UNIX systems. The new software will access these values from header keywords in the SPT file where formerly system-dependent binary disk files provided the values.

FITS2GEIS changes:

- FITS2GEIS drops the '/ GROUP PARAMETERS: OSS' heading comment. There are no group parameters in the FITS file, and when they are created in FITS2GEIS the heading comment is left out.

- The FITS standard FILENAME keyword is present in the FITS files, but is stripped out by FITS2GEIS.

FILENAME= 'x3i00206t.d0h'      / name of file

How to identify OPUS 10.0 headers for WFPC2 and FOC:

FLTSWVER and OPUS_VER keywords, which are in the STIS and NICMOS FITS spt headers, are not in WFPC2 or FOC shh. KWDB OPR 38754 has been filed to add these useful keywords to the WFPC2 and FOC shh file. This will probably be done for OPUS 10.1, but in the meantime, to identify an OPUS 10.0 header:

In the old science file but not in the new, you will find the following right after the group parameters and before the "real" keywords:

PSIZE49 =                   32 /

        / GROUP PARAMETERS: OSS

        / GROUP PARAMETERS: PODPS

        / GROUP PARAMETERS: DATA QUALITY FILE SUMMARY

        / GROUP PARAMETERS: PHOTOMETRY

        / GROUP PARAMETERS: IMAGE STATISTICS

        / WFPC-II DATA DESCRIPTOR KEYWORDS

INSTRUME= 'WFPC2             ' / instrument in use

This is what the user would see on getting the waivered fits files out of the archive and translating them to geis files by the use of strfits. (If he/she looked at them coming out of OPUS before being converted to waivered fits by the archive, he/she would see these comments properly distributed among the group parameters in the old data, but not in the new.)