***** File HDRFORM.TXT FITS Header Descriptions The International Halley Watch agreed early in the project that all data would be submitted from the individual Disciplines to the Lead Center using the FITS format (Wells et al., 1981). When the decision was made to distribute this information on CD-ROM, it was determined that the data had to have even broader accessibility. For this reason the original FITS files, with contiguous headers and data, were split into separate files distinguishable by their filename extensions (.HDR for headers). The file sizes were preserved as multiples of 2880 bytes, allowing the original FITS byte stream to be recovered by concatenating the appropriate header and datafile. PDS labels were constructed to allow definition of the datafiles for the Planetary Data System. For each datafile there must always be an associated FITS header. The convention for naming files on the IHW CD-ROMs was proposed by the Lead Center and NASA/Goddard Space Flight Center (GSFC) personnel to include a unique data qualifier for the data. Specifically, a set of subnet codes was established to enable identification of the IHW Discipline/subdiscipline from the filename itself. A CD-ROM running number and file extension complete the filename (example: LSPN0059.HDR). A short list of this convention by Discipline and subnet (or experiment) is given below (for headers only): PDS Object FITS Discipline Subnet File Ext (description) NAXIS = Code ______________________________________________________________________ text 1 Astrometry ASTR .hdr fits_label (no data) 0 IR Stduies IRSP .hdr table (filter) 0,2 IR " IRFT .hdr table(photometry) 0,2 IR " IRPH .hdr table(polarimetry) 0,2 IR " IRPOL .hdr spectrum(filter) 2 IR " IRFC .hdr spectrum 2 IR " IRSP .hdr image 2 IR " IRIM .hdr fits_label (no data) 0 Large Scale Phen LSPN .hdr image(browse) 2 Large " LSPN .hdr image 2 Near Nucleus NNSN .hdr table (narrow band) 0,2 Photometry Polar PFLX .hdr table (broad band) 0,2 " PMAG .hdr table (polarization) 0,2 " PPOL .hdr table (Stokes parameters) 0,2 " PSTOKE .hdr fits_label (no data) 0 Radio Studies RSCN .hdr fits_label (no data) 0 " RSSL .hdr spectrum 1 " RSSL .hdr spectrum(multiple) 1 or 2 " RSOH .hdr spectrum(multiple) 2 " RSRDR .hdr image 2 " RSCN .hdr image(multiple) 3 " RSOC .hdr spectrum (visibility) 6 " RSCN .hdr spectrum (visibility) 6 " RSOH .hdr spectrum (visibility) 6 " RSSL .hdr spectrum 1 Spectroscopy SPEC .hdr spectral image qube 2 " SPEC .hdr image 2 " SPEC .hdr fits_label (no data) 0 Amateur AMDR .hdr fits_label (no data) 0 " AMPG .hdr fits_label (no data) 0 " AMSP .hdr table (magnitude) 0,2 " AMV .hdr table (radar) 0,2 Meteor MSNRDR .hdr table (visual) 0,2 " MSNVIS .hdr ______________________________________________________________________ A table linking the subnet codes above and the subdiscipline names is given in Section 5 ('Filenaming Conventions') of the file HALGUIDE.TXT. Concerning the numeric portion of filenames, calibration files for IRIM, IRSP, LSPN, and SPEC begin at 4001, whereas the Halley data themselves for all disciplines and subdisciplines start at 0001. The file extensions follow suggestions by the Planetary Data System (SPIDS v1.1; Martin et al., 1988) for tabular and image data. In addition, for IHW FITS, the original headers and data were split into separate files, with header filename extensions as listed below. .HDR - FITS header records We have conformed with the PDS definition of a specific keyword to indicate the presence of a FITS header (the keyword TYPE = FITS) when the "data" object is a foreign label (FITS_LABEL). In FITS, if NAXIS=0, then no data records need follow, as in the case of an upper limit. The "dataless" headers can be recognized by the NAXIS value or the IHW keyword DAT-FORM = NODATA in the FITS HEADER. The PDS label (with same filename but differing extension) points at the HEADER file as its data object. As shown in the above table, the "dataless" header can occur for different types of data: images (LSPNNNNN or IRIMNNNN), spectra which can be ordered groups (IRSPNNNN) or standard (RSSLNNNN), and existing but not archived data as for AMDRNNNN, AMPGNNNN, AMSPNNNN. REFERENCES Martin, T.Z., Martin, M.D., Davis, R.L., Mehlman, R., Braun, M., Johnson M.: October 3, 1988, Standards for the Preparation and Interchange of Data Sets, Version 1.1, JPL D-4683. Wells, D.C., Greisen, E.W., and Harten, R.H.: 1981, Astron. Astrophys. Suppl. Ser. 44, 363.