Data Set Overview
      =================
      This data set presents the fluxes derived from narrow band
      photometry of Comet 1P/Halley as part of the International
      Halley Watch (IHW) Photometry and Polarimetry Netword (PPN).
      Standard filters, reference stars and reduction procedures
      were used as far as possible to reduce all narrowband data
      submitted to the PPN.  The original data have been reformatted
      data supplied as addenda to the original submission have been
      added and the accompanying documentation updated in this revised
      version.
 
      The data are in tabular form, and are presented as a single
      summary table sorted chronologically.  Information identifying
      the original source file from version 1 of this data set has
      been included for historical reference.
 
      Filters
      =======
      A standard narrow-band filter set, already in development
      prior to the IHW, was formalized and extended during the
      Halley Watch project.  The general filter parameters were
      summarized in tables in Sekanina (1991)  ('JPL D-400-450'
      in the reference list), and have been included in the
      documentation files of this data set.
 
      An initial set of five filters was manufactured and
      distributed at the beginning of the IHW period:
 
          3650 A   Continuum
          3871 A   CN
          4060 A   C3
          4845 A   Continuum
          5140 A   C2
 
      A second set of filters was added as they were produced
      after the start of the Halley Watch:
 
          3085 A   OH
          4260 A   CO+
          6840 A   Continuum
          7000 A   H2O+
 
      In addition, three observatories (Lowell, Cerro Tololo and Perth)
      also made use of an existing NH filter centered at 3365 A.
 
      Standard Stars
      ==============
      A set of standard stars specifically selected for narrowband
      photometry of comets was defined and distributed to PPN
      observers.  An organized campaign to observe suitable
      standards using the IHW filter set took place in two
      parts: first, Zellner and Wisniewski (1985) observed
      standards using the initial set of five filters; second,
      the PPN disipline specialists themselves as well as a number
      of colleagues undertook a campaign to establish standard
      star magnitudes for the filters not included in the work
      of Wisniewski and Zellner (1985).  A summary of this
      second observing program is in Osborne et al. (1990).
 
      Data Reduction
      ==============
      In order to minimize variations due to differences in local
      reduction procedures (in calculating airmass, for example),
      the PPN requested observers submit instrumental magnitudes
      outside the atmosphere, and completed the reduction to
      magnitude and flux using a single standard technique,
      described in detail in Sekanina (1991) ('JPL D-400-450' in
      the reference list).  Where possible, data that were received
      in a more advances state of reduction were back-processed to
      the instrumental magnitude stage and rereduced using the
      standard procedures.  Thus, values for fluxes, errors and
      airmasses may vary substantially in this data set from those
      present in the original file submissions of version 1.
 
      Modification History
      ====================
      The first version of this data set contained 2500 sets of
      individual observation files.  Each individual observation
      was a table of results from a specific observer using a
      particular system (observatory + telescope + detector)
      on a single night.  For each such file, there was a PDS label
      file, a FITS table header file detached from the data, and
      the FITS table data segment.
 
      After the first version was archived, personnel at the PDS
      Small Bodies Node (SBN) re-reduced a large part of the data
      using the standard technique described in 'Photometry and
      Polarimetry' chapter of 'The Comet Halley Archive Summary
      Volume' (cited in the reference list as 'JPL 400-450').  An
      abbreviated list of notes about specific reprocessing was
      created as an HTML errata file displayed on the SBN archive
      pages.  A summary table of all results was also created and
      offered as an 'index table'.
 
      To create version 2, SBN personnel did the following:
 
        o  Observer, telescope and observatory information was
           recovered from the FITS headers and inserted into the
           'index table'.
 
        o  Observing times in the 'index table', originally
           stated as day number and fraction, were converted to the
           ISO standard time format (yyyy-mm-ddThh:mm:ss).  Day
           fractions were always supplied with at least four
           significant digits (five in some unusual cases).  Note
           that, therefore, times are never more accurate than the
           nearest second, and typically are only accurate to
           +/- 5 seconds.
 
        o  A check of 'index table' lines vs total observations in the
           original FITS tables revealed a discrepancy of 25 lines
           submitted but not included in the 'index table'.
           These were accounted for thus:
 
                - Three files, each with eight record - pflx2285,
                  pflx2370 and pflx2388, contained no aperture size
                  information in the original submission.  A subsequent
                  errata list stated that these files were 'accidentally
                  included' in the original archive.
 
                - One file, pflx1326, had an incorrect value of NAXIS2
                  in the FITS header, resulting in the last record (of
                  11) being omitted from the reprocessing of the file.
 
           All of these records are also omitted from the final summary
           table.
 
        o  The original PDS and FITS files were discarded.
 
        o  Addenda, submitted after the original archive was complete,
           were incorporated into the summary table.
 
      30 October 2006, A.C.Raugh

Confidence Level Overview
      =========================
      Because these observations were rereduced by the IHW Photometry
      and Polarimetry Network (PPN) personnel, errors have been
      calculated for each flux in a uniform way wherever sufficient
      information was available.  See Sekanina et al. (1991)
      ('JPL D-400-450' in the reference list') for details of the
      reduction process and error propagation.
 
      Note that, because times were reported as day fractions with
      only four (or sometimes five) significant digits, all time
      values listed anywhere in this data set - data files, labels,
      or elsewhere - are never accurate to more than one second, and
      are typically accurate to only +/- about five seconds.
 
      Also, the following comment was included among the errata for
      these data:
 
         For a number of NARROW BAND measurements, the integration
         times are not given; in these instances the original
         submissions only reported 'average' values.