| DATA_SET_DESCRIPTION |
This data set description was prepared by Stephanie McLaughlin and
is based on the documentation provided by Carey Lisse and
included in this archive.
Data Set Overview
=================
This data set contains 12-, 25-, 60-, and 100-micron photometry of
the dust coma of comet 9P/Tempel 1 during its 1983 apparition.
The photometry was derived from reconstructed observations acquired
by the Focal Plane Array (FPA) instrument on the Infrared Astronomical
Satellite (IRAS). The types of observations were Sky Survey Atlas
(ISSA) scans and Additional/Pointed Observations (AO). A comprehensive
discussion of these data was provided by Carey Lisse and included as
documentation. The reconstructed images used for this photometric
analysis are available in the PDS data set
DI/IRAS-C-FPA-5-9P-IMAGES-V1.0.
These data support the analysis of the dust environment of Tempel 1
for the NASA Deep Impact Mission (Lisse et al. 2005 [LISSEETAL2005]).
Background
----------
IRAS imaged comet 9P/Tempel 1 during the months before and after
perihelion on July 9, 1983. IRAS spent the majority of its
observing time in the survey mode that systematically mapped
the sky with a series of overlapping and confirming ISSA scans
(Wheelock et al. 1994 [WHEELOCKETAL1994]). However, IRAS also
devoted time to making pointed observations (A0) of selected
fields of interest (Young et al. 1985 [YOUNGETAL1985]). IRAS
observations were acquired by its Focal Plane Array, a
multi-wavelength detector with spectral bands centered nominally
at 12, 25, 60, and 100 microns (Beichman et al. 1988
[BEICHMANETAL1988]).
To support analysis of the dust coma of comet 9P/Tempel 1, Russell
Walker selected sets of AO and ISSA images archived at the Infrared
Processing and Analysis Center (IPAC), then corrected the images
for the effects of extended source emissions. Walker delivered the
reconstructed, in-band radiance images and noise maps to the Deep
Impact project. These data are archived in PDS as data set
DI/IRAS-C-FPA-5-9P-IMAGES-V1.0.
Walker provided aperture photometry of Tempel 1 with his delivery
of reconstructed IRAS images. However, a preliminary review of
the photometry determined that the background subtraction method
could be improved. Lisse developed an algorithm that better
simulated the background then used this method to derive the
photometry in this data set.
Processing
==========
The following reconstructed, in-band radiance images were used
to derive the photometry:
AO
--
SOP OBS UTC Date Bands (micron)
=== === ===================================== ===============
287 13 1983-06-18, 21.50 days pre-perihelion 12, 25, 60, 100
407 12 1983-08-17, 38.50 days post-perihelion 12, 25, 60, 100
407 43 1983-08-17, 38.75 days post-perihelion 12, 25, 60, 100
509 40 1983-10-07, 90.00 days post-perihelion 12, 25, 60, 100
510 22 1983-10-08, 90.25 days post-perihelion 12, 25, 60, 100
where SOP = satellite operations plan and OBS = observation number
ISSA
----
Mean SOP Mean UTC Date Bands (micron)
======== ====================================== ===============
339 1983-07-14, 4.50 days post-perihelion 12, 25, 60, 100
368 1983-07-28, 19.25 days post-perihelion 12, 25, 60, 100
389 1983-08-08, 30.00 days post-perihelion 12, 25, 60, 100
421 1983-08-24, 46.00 days post-perihelion 12, 25, 60, 100
493 1983-09-28, 81.25 days post-perihelion 12, 25, 60, 100
where Mean SOP is the average satellite operations plan used to
identify a specific, reconstructed survey scan
For sky background removal, Lisse applied an algorithm that employed
a 2-dimensional quadratic surface fit to a synthetic background,
created by taking the in-band radiance image and replacing all
pixels within a certain pixel radius, centered at the nucleus,
with the median value of the image. The masked region size was
chosen to eliminate any contamination of the background by cometary
emission. The background surface fit was then subtracted from
the original in-band radiance image.
For photometry, circular apertures of increasing radii were sampled
until the summed in-band radiances reached an asymptote. The results
were recorded in ASCII tables, one for each in-band radiance image.
For more information about these processes, refer the explanatory
supplement included with this data set.
Parameters
==========
The aperture photometry data are ASCII tables with fixed-length
records. Each table contains five columns of data: aperture radius
in pixels, aperture radius in arcseconds, total in-band radiance for
the circular aperture, median value for the subtracted background,
statistical noise in the summed in-band radiance. In-band radiance,
background, and noise are recorded in units of Watts/cm^2/steradian.
The naming convention for the AO aperture photometry tables is
sSOP_oOBS_BANDum_phot.tab where SOP is the satellite operations
plan number, OBS is the observation number, and BAND is the
wavelength in microns.
The naming convention for the ISSA aperture photometry tables is
sMEANSOP_BANDum_phot.tab where MEANSOP is the average satellite
operations plan number and BAND is the wavelength in microns.
Data
====
One photometry table corresponds to one reconstructed, in-band
radiance image. The PDS label includes the file name of the
radiance FITS image used to derive the photometry.
The first record in each photometry table is intentionally set
to zeros because it is the true zero point for the photometry.
Media/Format
============
This data set is released as a logical data volume.
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