***** File FITSFORM.TXT FITS File Descriptions The International Halley Watch agreed early on 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). In order to distribute the data on CD-ROM, this original form was sometimes adapted to easier file access by splitting the header from the data, e.g., files with extensions .hdr and .dat, while preserving the 2880 byte stream. In other cases, the files were simply copied directly to the medium; these files carry the extension .fit. The convention for naming files on the CD-ROM was proposed by the IHW Lead Center to include a unique data qualifier for the data. A specific set of rules was established to identify the net and subnet for each discipline (given by a letter code). A CD-ROM running number relates the information contained in the various indices to the files containing the actual data. A short list of this convention by discipline and subnet (or experiment) is given below: PDS Object FITS Discipline Letter File Ext (description) NAXIS = Code text 1 Astrometry ASTR .fit table (filter) 0,2 IR Studies IRFT .fit table(photometry) 0,2 IR " IRPH .fit fits_label (no data) 0 Large Scale Phen LSPN .fit image 2 Large " LSPN .fit image 2 Near Nucleus NNSN .fit table (broad band) 0,2 Photometry Polar PMAG .fit table (narrow band) 0,2 " PFLX .fit table (polarization) 0,2 " PPOL .fit fits_label (no data) 0 Radio Studies RSCN,OH,SL .fit spectrum 1 " RSOH .fit spectrum(multiple) 2 " RSOH .fit image 2 " RSCN .fit spectrum 1 Spectroscopy SPEC .fit image 2 " SPEC .fit table (magnitude) 0,2 " AMV .fit Note that the Subnet coding (explained in the Filenaming Conventions) is one way to distinguish file extension and content. The file extensions follow suggestions by the Planetary Data System: .fit - FITS records of 2880 bytes In FITS, if NAXIS=0 (no extension) then there are no data records. The "dataless" headers can be recognized by the NAXIS value or the IHW keyword DAT-FORM = NODATA in the HEADER. "Dataless" header can occur for different types of data: images (LSPNNNN.IMG), and spectra which can be ordered groups (SPECNNNN.DAT) or multiple (RSCNNNNN.DAT). Wells, D.C., Greison, E.W., and Harten, R.H.: 1981, Astron. Astrophys. Suppl. Ser., 44, 363.