The output files for the IUE Final Archive are fundamentally different from those produced by IUESIPS, both in content and format. They are based on the Flexible Image Transport System (FITS) format (NOST 1995) and incorporate the FITS binary table extensions (NOST 1995) and FITS image extensions (Ponz, Thompson, and Muñoz 1994). Although some FITS reading routines may not yet support these new FITS extensions, it was felt that there was no convenient alternative FITS format available for storing IUE data. Note that only those features included in the basic binary table proposal (i.e., excluding the conventions described in the appendices of the proposal) have been used in the Final Archive file formats. The formats described below (as originally described in DCG 1995) have been approved by the IUE Three Agencies as well as the NOST FITS Support Office.
Because NEWSIPS data will be made available to the astronomical community via electronic transfer, the adopted FITS format is envisioned as both a disk file format and a tape file format. It should be pointed out, however, that disk file structures vary with operating systems. For this reason, users should consider the Final Archive data as being comprised of 2880-byte logical records which may or may not be identical to any physical record lengths. FITS files transferred to VAX VMS systems using FTP for example, typically have 512-byte rather than 2880-byte records.