Data Set Overview
  =================

  This data set is intended to include all reported timings of observed
  asteroid, planet, and planetary satellite occultation events, as well as
  axes derived from those timings by David W. Dunham and David Herald.  Most
  of these timings are unpublished and have been collected by Dunham and
  Herald.  This version is complete through the end of 2015.  (The planet data
  are located along with the satellite data in the occsatlist and occsattime
  files.)

  The sizes (major and minor axes) derived from the occultation timing data
  are the result of an analysis program by Dunham and Herald, applied
  consistently to all the occultation events.


  Occultations Analysis Program
  =============================

  As input to the analysis, observers submit a report to the program
  including disappearance and reappearance timings, observatory
  location, and observing conditions.  The observations are reduced using the
  Besselian fundamental plane as the reference plane. The basic methodology is
  as follows.

   - The position of the asteroid is computed at three intervals, centered on
  the nominal mid time of the observed occultation. The positions are
  converted to (x,y) coordinates on the fundamental plane, expressed as a
  quadratic expression. These calculations are performed in the J2000
  reference frame.

   - The (x,y) position of each observer on the fundamental plane is computed
  at each of their event times. The orientation of the fundamental plane is
  referenced to the apparent equinox of date for this purpose.

   - All of the observer positions are referenced to a moving reference frame
  that is fixed relative to the asteroid. This reference frame has a nominal
  zero defined by the observer coordinates associated with the first
  observation. The motion of the reference frame is that of the asteroid.

   - The fit of an ellipse to the observations occurs in this moving reference
  frame (which is fixed relative to the asteroid). The calculations are
  performed in units of earth radii, and converted to km for output purposes.

   - The astrometric position of the asteroid is obtained by combining the
  motion of the moving reference frame with the location of the fitted ellipse
  on that reference frame, to obtain the time when the asteroid was closest to
  the geocenter - from which the time, separation and position angle of the
  asteroid relative to the star are derived.

  This methodology takes full account of the motions of the asteroid and the
  observers.


  Data
  ====

  The asteroid occultation timing data are collected into two files. The
  occlist file lists one occultation per line, along with the identification
  of the asteroid and star, and additional information about the star
  including RA and dec.  These lines also include the major and minor axes
  derived from the timings for that occultation, if any, along with
  information about the analysis.  The list is chronological, with an
  occultation ID assigned to each one.  The occtimings file lists the
  individual timings measured for each occultation, with one disappearance and
  reappearance per line, as well as information about the observing site and
  the observational circumstances.  The latitude, longitude, and elevation of
  each site are included.

  Two analogous files, occsatlist and occsattime, with occultation data on
  planets and planetary satellites, are also included.

  Kepler2 star cross-reference:  The Kepler2 mission is looking at fields
  around the ecliptic.  Asteroidal occultation light curve provides a
  relatively high resolution light curve of the star - better than can be
  obtained by most (if not all) other ground-based techniques (including
  speckle) [INVALID_PDS_CHARACTER] thereby providing info that may be of use
  in the analysis of K2 data.  A link/flag between stars observed in an
  asteroidal occultation with stars that have been selected as target stars in
  the Kepler2 mission has now been included in the files occlist and
  occsatlist. The list of Kepler2 target stars is growing as new fields become
  defined, so this information will be updated in future years.


  Ancillary Data
  ==============

  Summary files, occsummary.tab and occsatsummary.tab, contain the major and
  minor axes and position angles from the elliptical or circular fits for all
  events with fit quality code 2 or greater, extracted from occlist and
  occsatlist respectively.

  Graphics image files show plots of the occultation fits for those events
  with fit quality code 2 or greater.  These image files are located in the
  document directory, and are accompanied by a descriptive text file
  0Graphics.asc explaining how the plots are to be read.  The filenames of the
  image files concatenate the asteroid number, asteroid name or provisional
  designation, and occultation date.


  Modification History
  ====================

  The first version of this data set, introduced in 2003, included
  occultations only through 1998.  The update of 2004 not only adds
  occultations through March 1, 2004, but also provides a more systematic
  arrangement of the data.  The data set was updated annually since then.  The
  number of asteroid occultations included in each successive version is as
  follows:

     Year:   Version:  Number of occultations:
      2003    V1.0      183
      2004    V2.0      524
      2005    V3.0      680
      2006    V4.0      865
      2007    V5.0     1055
      2008    V6.0     1203
      2009    V7.0     1417
      2010    V8.0     1662
      2011    V9.0     1935
      2012    V10.0    2102
      2013    V11.0    2275
      2014    V12.0    2469
      2015    V13.0    2717
      2016    V14.0    2933

Confidence Level Overview
  =========================
    This data set is compiled from the observations made by a large number of
    observers.  Indications to the confidence level of each observation are
    included in the data files.

    For three of the occultation entries, the latitude and/or longitude of the
    observation is out of range, and so far it has not been possible to get
    corrected values.  The affected observations are as follows:

    690 Wratislavia 1982 Nov 14
    1Andrew Lowe, Androssan, Alberta -113  2 87. +53 38 11. 692* 94054.6 D 941
    7.8 R

    324 Bamberga 1987 Dec 8
    1K Kaufman, Humble TX - 95  2 45.1 +30 0 99.9 21* 20 123524.2 M 123524.2 M
    2 1.00

    25 Phocaea 1998 May 13
    3B.Peters/R.Peterson, Arizona City, AZ -111 43 93. +32 27 70. 523* 25319.5
    D 25326.3 R 4

    (Longitude and latitude in degrees, minutes, seconds are immediately
    following the address.  Note seconds values greater than 60.)