| DATA_SET_DESCRIPTION |
Data Set Overview
=================
The data presented with this data set include:
1) SIGHTING.TAB - contains a listing of 8210 individual sightings
associated with 2004 asteroids. SIGHTING.TAB
contains the observation index, the
identification of asteroids sighted, information
pertaining to observation times, positional
information on the observations of asteroids
detected, geometric albedos, diameters and their
associated uncertainties, input values used in
the calculations of the geometric albedos and
diameters using the asteroid standard thermal
model, the observed flux densities in each band,
detector crossing information, correlation
coefficients, and status flags for reduction
steps.
2) DIAMALB.TAB - contains averaged radiometric diameters and
geometric albedos derived from individual
observations for 1796 numbered asteroids and 88
unnumbered asteroids (as of 1983) whose orbital
elements were determined using astrometry from
two or more apparitions.
3) SINGLE.TAB - contains an entry for each of 120 asteroids for
which there is an accepted sighting, but in one
band only. This file includes the absolute
visual magnitude of the asteroid, the albedo and
diameter derived from the measurement and their
associated uncertainties, and the accepted
status word.
4) GRNDDAT.TAB - contains entries for each of 4677 numbered
asteroids and 2632 unnumbered asteroids (as of
1985) for which associations were sought in the
IRAS data. Asteroids 719 Albert and 878 Mildred
were still lost as of 1985 and are not included.
These entries include an initial estimate of
geometric albedo and diameter used in processing
IRAS survey observations of asteroids, the
adopted taxonomic classification, and the
orbital elements at three epochs. The Julian
dates of the epochs are 2445400.5, 2445500.5,
and 2445600.5. For further information regarding
these data see Tedesco, et. al., 1992
[TEDESCOETAL1992].
5) IMPSSTAT.TAB - contains a summary of the number of times each
asteroid was predicted to be scanned, and
possible reasons for any failure to be detected.
It contains entries for each of 4677 numbered
asteroids and 2632 unnumbered asteroids (as of
1985) for which associations were sought in the
IRAS data. Asteroids 719 Albert and 878 Mildred
were still lost as of 1985 and are not included.
These entries include the number of predicted
sightings, number of accepted sightings, number
of rejected sightings, number of missed
predicted sightings, number of missed predicted
faint sightings, number of dead 25 micron
detector non-detections, number of noisy 25
micron detector non-detections, number of missed
predictions in the galactic center region, and
other non-detections.
6) REJECT.TAB - summarizes the number of rejected sightings for
each asteroid and possible reasons for
rejection.
7) MISSED.TAB - contains a summary of those asteroids which were
predicted to pass across the IRAS focal plane
during survey mode, but which generated no
accepted associations. Entries include the
number of times an asteroid was predicted to be
scanned but was missed, and the derived greatest
lower limit on the albedo and least upper limit
on the diameter, plus a status word detailing
the circumstances of the observation failure.
8) STMODEL.TAB - contains the flux look-up table used to generate
the IMPS albedos. This table was provided by L.
Lebofsky and was derived from the IRAS standard
thermal model.
In the original release of the IMPS data products, a number of
'derived status word (ADSTAT)' bits were always set to zero (flag
not set), and have been excluded here, these were:
ADSTAT 1 - All bands. Not used. Always zero.
ADSTAT 2 - All bands. Not used. Always zero.
ADSTAT 3 - All bands. Not used. Always zero.
ADSTAT 5 - All bands. Not used. Always zero.
ADSTAT 6 - All bands. Not used. Always zero.
ADSTAT 7 - 100 micron band. No albedos derived from individual
observations in this band were rejected from the final average
using Chauvenet's criterion, therefore this flag was always set
to zero for this band in this datafile.
ADSTAT 8 - 25 micron band. The albedo calculation for each
observation converged within 100 iterations, therefore this flag
was always set to zero for this band in this datafile.
In the original released IMPS data product, the bits in the ADSTAT
word were ordered from right to left.
A number of 'confusion status word (ASTCST)' bits were also always
set to zero (flag not set), and have been excluded here, these
were:
ASTCST 5 - Set after hours-confirmation. Since sightings
detections are only seconds-confirmed, this flag is always set
to zero.
ASTCST 6 - Set after hours-confirmation. Since sightings
detections are only seconds-confirmed, this flag is always set
to zero.
ASTCST 7 - Set to 1 when an analog to digital saturation flag was
set due to a bright source saturating at least one detector in
this band. No such events in IMPS in any band.
ASTCST 8 - Not used. Always zero.
In addition, a number of 'asteroid status word (ASTATW)' bits
were always set to zero (flag not set) or one (flag set) and
have been excluded here, these were:
ASTATW 5 - WSDB MCON position match. All MCON (WSDB 'weeks' or
months confirmed) asteroid sightings are rejected by IMPS.
These sightings are likely to be confused with stationary
background sources (e.g. molecular clouds, galaxies, knots of
infrared cirrus). See ASTATW 9. No accepted detections had flag
set.
ASTATW 8 - IMPS asteroid association. Set to unity for every
accepted asteroid sighting, therefore the flag is always one
in this file by definition.
ASTATW 9 - Point Source Ver. 2 match. All asteroid sightings
confused with sources in the IRAS Point Source Catalog are
rejected by IMPS. This is a subset of ASTATW 5.
ASTATW 10 - Detections only by small detectors on the outer edge
of the focal plane array. No accepted detections had this flag
set.
ASTATW 11 - Predicted flux < 0.14 Jy. Set a priori for all
candidate associations of an IMPS asteroid if no predicted flux
density at 25 microns is greater than 0.14 Jansky. No detections
were accepted when this flag was set.
ASTATW 16 - 100 micron albedo used in the final average albedo.
Since no 100 micron detections contribute to derived IMPS
average values, this flag is never set.
ASTATW 17 - Faint Source Version 2 match. All asteroid sightings
confused with sources in the IRAS Faint Source Survey are
rejected by IMPS (See MOSHIRETAL1992), therefore this flag is
always zero in this data file.
ASTATW 20 - Serendipitous Version 1 match. All asteroid sightings
confused with sources in the IRAS Serendipitous Survey Catalog
are rejected by IMPS (See KLEINMANETAL1986), therefore this flag
is always set to zero in this data file.
ASTATW 29 - Not used. Always zero.
ASTATW 31 - 2+ sightings match. Set if more than one source is
associated with a single asteroid prediction and therefore
rejected by IMPS. No detections were accepted in this file
when this flag was set.
ASTATW 32 - Not used. Always zero.
Modification History
====================
The IMPS data set was ingested in 1994 and updated to correct a
minor error in 1995. These versions included only FP102, the
diameters and albedos. The data set has now been updated to
include FP103, FP104, FP105, FP 106, FP107, FP108, and the flux
lookup table used tto generate the IMPS albedos.
As part of a general review of archive data in Feb 2002, the
labels and data files were examined and the following changes
made:
o Numbers were provided for all asteroids numbered
as of 15 Jan 2002. Numbers were found by referencing Ted
Bowell's cross-identification database, as incorporated
into the Small Bodies Data Base of the PDS Small Bodies
Node (SBN). Provisional identifications from the original
IMPS files were retained for cross-referencing.
o Names were provided for all asteroids named as of 02 Feb
2002. Names were gathered from the list provided by the
Minor Planet Center at this URL:
http://cfa-www.harvard.edu/iau/lists/MPNames.html
o All files listing asteroid observations except 'sighting.tab'
were re-sorted on asteroid number. Asteroids identified only
by provisional designation are located at the bottom of the
files, sorted by provisional ID. The 'sighting.tab' file was
and is sorted on sightings index number.
o Minor errors were corrected as found (e.g., the wrong value
for 'COLUMNS' was found in two labels; incorrect 'START_BYTE'
values were found in another).
o Potentially confusing references to 'FPA.LBL', a file from a
different data set, were replaced by a reference to the
appropriate PDS DATA_SET_ID.
o Cosmetic changes were made to bring labels and catalog files
into conformance with current PDS/SBN standards and practices.
o Documentation found in some of the labels regarding status
words which were systematically excluded from more than one
of the data files was extracted from those labels and
incorporated into the information above.
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