***** File AAREADME.TXT This compact disc (CD-ROM) is the last of a 5-disc set containing digital data obtained through the efforts of all the International Halley Watch (IHW) Disciplines and their corresponding Networks. Because of their multi-Discipline composition, the five discs, which are Volumes 19-23 in the total set of IHW CD-ROMs, have become known informally as the "mixed discs." Volumes 1-18 are dedicated to the Large-Scale Phenomena Discipline and its very large image files, which have been deposited on disc in compressed form. Finally, Volume 24 contains data from the IHW "Trial Run" targets--comets P/Crommelin and Giacobini-Zinner--and Volumes 25-26 are devoted to space data returned by the Halley intercept spacecraft and the International Cometary Explorer (ICE). This final "mixed disc," which contains the chronologically-last files of Halley ground-based data, differs from the previous mixed discs (Volumes 19- 22) in a number of ways. First, it serves as a "summary disc" in somewhat the same way that Volume 18 did for the set of Large-Scale Phenomena discs. To be specific, the following new directories appear on HAL_0023 (Volume 23): o CALIB Calibration files broken out by Discipline o DOCUMENT/OBSVTORY Tables of Observatories & Observing Sites o IR_FILTER Infrared Filter Curves o METEOR Entire set of Meteor Discipline Data o SOFTWARE/BROWSE Source code for constructing L-SP Browse Images o SOFTWARE/COMPRESS Source code for compressing L-SP Imagery o SOFTWARE/DECOMP Source code for decompressing L-SP Imagery o SUMMARY/ERRATA Errata Files for each IHW Discipline o SUMMARY/INDEX "Quick Look Index" & "Pathtable" for each of 5 "Mixed Discs" o SUMMARY/OTHER Replacement files for VOLDESC.SFD files on Volumes 19-22 Although the calibration files also appear in the standard data directories on Volumes 19-23, chronologically interspersed with the Halley data, it was thought important to break them out in a dedicated area on the last mixed disc. Had they been less voluminous, the Infrared filter curve data could have been placed in that Discipline's Appendix write-up; separate placement on this disc seemed a good alternative. Although some of the Disciplines included lists of contributing observatories in their Appendices (deposited on all 5 mixed discs), only the DOCUMENT/OBSVTORY directory on this disc gathers all IHW Observatory information together in one place. Data from the Meteor Studies Discipline is present on all the mixed discs in the form of large indices (one each for Radar and Visual observations), but only on this disc are the original FITS headers and table extensions present. The new software directories listed above include files also deposited on the L-SP CD-ROMs (Volumes 1-18); they have been included here mostly for redundancy. Very important are the SUMMARY directories: /ERRATA contains all information of which we are currently aware concerning errors and irregularities in this Archive; /INDEX contains corrected versions of each of the "Quick Look Indices" and "Pathtables" resident on this and the other four mixed discs; and /OTHER contains replacement files for the VOLDESC.SFD files of Volumes 19-22, which had truncations in some of the lines. Should an archive user wish to construct one global quick look index or path table for the entire IHW Archive (excluding the L-SP data files on Volumes 1-18), concatenation of the QUIK_0nn.IDX or PATH_0nn.IDX (nn=19-23) files in /SUMMARY/INDEX would be the way to proceed. The QUIK_0nn.IDX indices on Volumes 19-22 had some (mostly minor) errors (cf. the file /SUMMARY/ERRATA/INDXERRS.TXT) which have been corrected in the /SUMMARY/INDEX versions here; hence the latter should be used whenever possible. The second way in which this CD-ROM differs from the previous four mixed discs concerns the documentation: that which is repeated from the other discs (the majority) has been improved and corrected when necessary, and there are some completely new files here as well. We cannot emphasize strongly enough that this CD-ROM, HAL_0023, should be used as the standard source of documentation and information, the other mixed discs (and this one as well) serving as the repository of particular data files of interest. In addition to the "new" directories just discussed, this disc contains a wide variety of supporting files and tools for the Archive user which are essentially identical to those on Volumes 19-22; the major categories are documentation, ephemeris information, searchable tables and indices, and software (source code as well as executable modules). These have been organized into four principal directories one level below the root: DOCUMENT, EPHEM, INDEX, and SOFTWARE. It is suggested that the Archive user review the document files listed below before roaming through the multi-level data directories: /DOCUMENT/HALGUIDE.TXT Brief guide to use of discs /DOCUMENT/CDTREE.TXT Schematic, annotated layout of disc /DOCUMENT/VOLINFO.TXT More complete description of disc, history of IHW CD-ROM generation /DOCUMENT/APPENDIX/*.APX Appendices for (all) nine IHW Disciplines /INDEX/INDXINFO.TXT Description of basic indices /INDEX/NETABLES/NETINFO.TXT Description of "printed archive" and Discipline-specific indices /SOFTWARE/SOFTINFO.TXT Brief enumeration of software on disc The time period covered by this disc is 1987 April 4 -- 1989 April 12. Data from all IHW Disciplines are included; as on the other mixed discs, the included L-SP data consist of subsampled, "browse" versions of the much larger compressed data files deposited on Volumes 1-18. Astrometry data from the previous apparitions of 1835 and 1910 have been put on this disc, as well as data from the "current" (1985-86) apparition. Data preparation for the IHW Archive has been the work of many people within each Discipline, of the Lead Center personnel at JPL, and of those at NASA/GSFC who actually generated the CD-ROMs. Efforts at the Discipline level are described in the Appendix files in the /DOCUMENT/APPENDIX directory, and a history of IHW CD-ROM generation is given in the ACKNWLDG.TXT file of the root directory and in the file /DOCUMENT/VOLINFO.TXT. Although many people have been involved in this project (including the observers), the individuals listed below were responsible for actually making the discs and they accept responsibility for any errors in disc format and/or layout, but not actual file content. All of the text files on this disc have fixed length records padded to either 80 or 132 bytes per record. The last two characters of each record are a carriage return and line feed. This has been done to files with the following extensions (*.txt, *.str, *.apx, and *.lbl). M. Niedner, Jr. E. Grayzeck, Jr. IHW Discipline Specialist Small Bodies Node of for Large-Scale Phenomena Planetary Data System Laboratory for Astronomy Astronomy Department and Solar Physics University of Maryland Code 684.1 College Park, MD 20742 NASA/GSFC Greenbelt, MD 20771 D. Klinglesmith III A. Warnock III IHW Team Member for IHW Team Member for Large-Scale Phenomena Large-Scale Phenomena Laboratory for Astronomy Hughes STX Corporation and Solar Physics Code 631 Code 684.0 NASA/GSFC NASA/GSFC Greenbelt, MD 20771 Greenbelt, MD 20771 M. Aronsson IHW Lead Center Jet Propulsion Laboratory MS 169-237 4800 Oak Grove Dr. Pasadena, CA 91109