Each image has an associated RI VICAR header, which was generated by the
IUE Operations Control Center (IUEOCC) software during image
acquisition and contains various scientific and engineering data
pertinent to the image. This header, called the image label, consists of
72-byte lines containing EBCDIC and binary information as described in
|1-2||Image info. written by the system||EBCDIC|
|10-32||Real-time command buffer||EBCDIC|
|36-37||GO information from POT tape||EBCDIC|
|51-75||Data quality bits||Binary|
|83-85||Orbital elements and S/C info||EBCDIC|
|101-end||Databank parameters/IUESIPS Process History||EBCDIC|
The image label, as well as any appendages which had been added by IUESIPS for database information or label corrections, is stored in the primary FITS header. Each line contains the original label information coded in ASCII, in bytes 9 to 80, with blanks in bytes 1 to 8. Lines originally coded in EBCDIC have been converted to ASCII, and lines containing binary data have been converted into 2 lines containing hexadecimal ASCII characters (e.g., the unsigned integer byte value 63 will become `3F'). The first line of hexadecimal ASCII characters contains bytes 1 through 33 of the original line of binary data and is stored in columns 9 through 74. The second line contains bytes 34 through 66 in columns 9 through 74. The traditional VICAR line number and continuation character are stored at the end of each line in bytes 75 through 80. In this format, the image label generally consists of approximately 150 lines in the FITS header. Four COMMENT lines precede the image label, and one COMMENT line flags the end of the label.
Note that lines 3-9 were entered by the Telescope Operator (TO) at the console and may occasionally contain errors. Lines 36-37, normally input from the Preplanned Observation Tape (POT), may be modified by the TO and, hence, are also subject to errors. The automatic entries on the other lines (10-32) are more accurate but can be affected, for instance, by ground computer problems. The binary-format portion of the image label (located in lines 51-82 and 86-100) is not usefully decoded when interpreted in hexadecimal ASCII characters and has been omitted from the header examples shown in the following subsection. Further information concerning the contents of the image label can be found in the IUESIPS Information Manual, Version 2.0 (Turnrose and Thompson 1984) and the IUE Image Header Document (GSFC 1986). For a guide to the translation of the event round robin in the image label, see Van Steenberg (1989).