POSSIBLE WRONG COORDINATE SYSTEM TYPE IN ARECIBO FITS-HEADERS
POSSIBLE INCORRECT REQUESTED COORDINATES IN ARECIBO FITS-HEADERS
POSSIBLE INCORRECT COORDINATE OFFSETS IN ARECIBO FITS-HEADERS

Data affected: some FITS-files taken with CIMA 2.3 up to 2008-Apr-01
               some FITS-files taken with CIMA 2.2 and earlier versions
=======================================================================

A bug affecting the reported commanded coordinate system used and
coordinate offsets from the commanded center position has been
found. The problem only affects data taken with the telescope
commanded in horizontal coordinates (used by for example 'fixed
azimuth drifting').

Note that this bug only affects the values of the header parameters -
the data itself has been taken at the correct position.

The effect is that commanded coordinate system (FITS-header keyword
REQ_RADESYS) is reported to be galactic ("GAPPT") when the telescope
has been commanded in horizontal coordinates. This has happened for
all horizontal pointings made with CIMA version 2.3. For earlier
versions of CIMA the bug would only appear when the telescope has been
commanded from the 'AZ/ZA Pointing Control' window and the value of
REQ_RADESYS will then reflect the last pointing done before the 'AZ/ZA
Pointing Control' window was used.

When REQ_RADESYS has been incorrectly set to "GAPPT" in CIMAFITS-files
taken with CIMA 2.3, then the calculated offset values in FITS-header
keywords OFF_RA, OFF_DEC, OFF_AZ and OFF_ZA have all been wrong. This
bug has now been fixed.

When REQ_RADESYS has been incorrectly set in CIMAFITS-files taken with
CIMA 2.2 or earlier versions, the requested coordinates given in
FITS-header keywords REQ_RA and REC_DEC will refer to the last
commanded position that was NOT given from the 'AZ/ZA Pointing
Control' window. Also the calculated offset values in FITS-header
keywords OFF_RA, OFF_DEC, OFF_AZ and OFF_ZA will all been wrong. This
bug HAS NOT BEEN fixed.

A corrected algorithm was installed 1 April 2008. The version number
of the CIMAFITS-files has been updated from '1.09' to '1.10' to
reflect this correction.


DETAILED DESCRIPTION
--------------------

AFFECTED KEYWORDS:

The affected keywords are:

REQ_RADESYS        (coordinate system used for REQ_RA and REQ_DEC)
REQ_RA             (requested longitude in REQ_RADESYS system)
REQ_DEC            (requested latitude in REQ_RADESYS system)
OFF_RA             (RA J2000 offset to commanded center position)
OFF_DEC            (Dec J2000 offset to commanded center position)
OFF_AZ             (azimuth offset to commanded center position)
OFF_ZA             (zenith angle offset to commanded center position)

For CIMAFITS-files taken with CIMA 2.3, REQ_RADESYS will always be
incorrectly set to "GAPPT" whenever the telescope has been commanded
in horizontal coordinates. The requested coordinates REQ_RA and
REQ_DEC will, however, correctly contain the requested azimuth and
zenith angle values. The four offset values OFF_RA, OFF_DEC, OFF_AZ
and OFF_ZA will always be wrong and can't be used.

For CIMAFITS-files taken with CIMA 2.2 or earlier, REQ_RADESYS as well
as REQ_RA and REQ_DEC will reflect the last coordinates and coordinate
system used before the 'AZ/ZA Pointing Control' window was used. The
four offset values OFF_RA, OFF_DEC, OFF_AZ and OFF_ZA will always be
wrong and can't be used.

Note that the 'fixed azimut drift' mode was not affected by this
problem in CIMA version 2.2 or earlier, while it has been affected in
CIMA version 2.3.

Also, note that while the bug has been fixed for CIMA 2.3, it has NOT
been fixed in CIMA 2.2.


                                        Mikael Lerner

                                        Arecibo, 1 April 2008