urn:nasa:pds:smallbodiesoccultations
1.0
Asteroid Occultations V1.0
1.6.0.0
Product_Bundle
Dunham, D.W., Herald, D., Frappa, E., Hayamizu, T., Talbot, J., and Timerson, B.
2017
This data set is intended to include all reported timings of observed asteroid,
planet, and planetary satellite occultation events as well as occultation axes
derived from those timings by David W. Dunham and David Herald. This version is
complete through the end of 2016.
1911-08-14Z
2017-02-10Z
None
Individual Investigation
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Archive
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unpublished and have been collected by Dunham and Herald.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 2016. (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) -- 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 collected in a pdf file,
occ2017.pdf, located in the document directory.
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
2017 PDS4 V1.0 3224
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Primary
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