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Non-standard keywords
Besides the standard FITS keywords defined in the FITS documents, it is
possible to use other, non-standard keywords. Such non-standard
keywords have no global definition and may be interpreted differently
by different FITS readers.
A number of non-standard keywords has been used by ESO e.g. for
definition of frames acquired at the La Silla observatory. They are
given in Table 7.1.3 and should not be used with other
definitions. An extended set of FITS keywords are defined for
describing data from the VLT (see [7]).
Table 7.4:
Name translation between special non-standard FITS keywords and
MIDAS descriptors.
FITS keyword |
Data type |
MIDAS descriptor |
Remarks |
MJD-OBJ |
Real |
O_TIME(4) |
Modified Julian Date of start of exposure |
TM-START |
Real |
O_TIME(5) |
UT of start of exposure, in sec. after midnight |
TM-END |
Real |
- |
UT of end of exposure |
EXPTIME |
Real |
O_TIME(7) |
Exposure time in sec. |
RA |
Real |
O_POS(1) |
Right Ascension in degrees |
DEC |
Real |
O_POS(2) |
Declination in degrees |
POSTN-RA |
Real |
O_POS(1) |
Right Ascension in degrees |
POSTN-DE |
Real |
O_POS(2) |
Declination in degrees |
AIRMASS |
Real |
O_AIRM |
Mean airmass of exposure |
FILENAME |
String |
FILENAME |
Original file name |
ESO-LOG |
String |
ESO-LOG |
Observing log |
|
Due to the freedom to use non-standard keywords it is important to
know their exact definitions when transferring data between different
systems.
Next: Hierarchical keywords
Up: FITS keywords
Previous: Standard keywords
Petra Nass
1999-06-09