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XMM-Newton Science Analysis System Page: 1
movecalc
June 28, 2006
Abstract
CALCulate event coordinates in a MOVing reference frame
1 Instruments/Modes
EPIC MOS : all imaging modes
EPIC PN : all imaging modes
OM : Fast
2 Use
pipeline processing no
interactive analysis yes
3 Description
movecalc and the related task iauephem are intended to facilitate the spatial analysis of observation
data from moving objects such as comets or other solar system bodies. In still sky images generated
from aspect corrected X/Y coordinates the spatial distribution of events from these objects can be very
complex and depends on the projection of the object's track onto the image plane. This makes spatial
event selection very hard of even impossible in cases where the object is too faint to clearly stand out
against the X-ray background.
movecalc takes an event table with aspect corrected X/Y coordinate columns (as generated by task
attcalc) and adds two new columns X MOV/Y MOV (dierent names can be specied via parameters
xmovcol/ymovcol) containing the corresponding coordinates in a reference frame that is centered on
the moving object at all times. This requires a second input table which denes the track of the object
as a function of time. The table is created with the task iauephem and passed to movecalc via the
parameter objtrack. movecalc shall interpolate the object tracking data in time on an event by event
basis. This requires access to the event arrival times in a column TIME by default.
The new X MOV/Y MOV coordinate system is characterized by the following properties:
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 The origin coincides with the center of the moving object at all times.
 The orientation is that of the underlying X/Y system, i.e. +X MOV points east-wards and
+Y MOV to the celestial North pole.
 Each coordinate pair denes a point in a plane that is tangent to the celestial sphere (stan-
dard zenithal gnomic projection). The tangent point is given by the center of the moving
object at all times.
Please note: Geocentric parallax shifts are taken into account. This refers to the fact that the apparent
direction from the satellite to the object does in general not coincide with its geocentric position vector.
The eect is the bigger the closer the object is.
3.1 FITS/WCS considerations
Ordinary X/Y sky images have a FITS representation that adheres to the World Coordinate System con-
ventions specied in [1]. In practice this means that the conversion from tangent plane image coordinates
(X=Y ) to Right Ascension/Declination of the mean geocentric equatorial reference frame and vice versa
is uniquely given by the following set of column attributes:
attribute name meaning X/Y system X MOV/Y MOV system
TCTYPn type of projection RA--TAN/DEC--TAN RA--TAN/DEC--TAN
TCRVLn R.A./Dec of tangent point ra ref =dec ref 0/0
TCRPXn image coordinates of tangent point x ref =y ref 0/0
TCDLTn coordinate increment at tangent point
x=
y
x=
y
In the X MOV/Y MOV system the tangent point is moving with time. In the absence of a true FITS/WCS
standard for this situation the point is given the xed equatorial coordinate (0=0). This allows FITS
image viewers like Ds9 to display 'pseudo' sky coordinates for each image pixel which shall at least
be useful to estimate extents of structures in the X MOV/Y MOV image. Please note that the coordinate
increment in both systems is the same.
3.2 Usage examples
1. Add columns X MOV/Y MOV to table EVENTS in data set comet.ds. The track of the object is
dened in table comet track.ds:
movecalc table=comet.ds:EVENTS objtrack=comet_track.ds
2. Add columns X VAR/Y VAR to table EV in data set saturn.ds. The track of the object is
dened in table saturn track.ds:
movecalc table=saturn.ds:EV objtrack=saturn_track.ds xmovcol=X_VAR ymovcol=Y_VAR
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
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table yes table
name
name of existing table
A table specier which must point to an existing table in a data set that contains the columns specied
via parameters xcol/ycol. On successful exit the two columns named via parameters xmovcol/ymovcol
will have been added to the table
.
objtrack yes data set track.ds name of existing data
set
Name of a data set created by task iauephem which denes the position of the moving object as a function
of time.
xcol no column
name
X name of existing col-
umn in table table
The name of the column containing tangent plane projected X-coordinates of the events.
ycol no column
name
Y name of existing col-
umn in table table
The name of the column containing tangent plane projected Y-coordinates of the events.
timecol no column
name
TIME name of existing col-
umn in table table
The name of the column containing event arrival time tags.
xmovcol no column
name
X MOV valid column name
Name of the column to be added to the input table table containing X-coordinates of the events in the
moving reference frame; must be dierent from name of corresponding input column xcol.
ymovcol no column
name
Y MOV valid column name
Name of the column to be added to the input table table containing Y-coordinates of the events in the
moving reference frame; must be dierent from name of corresponding input column ycol.
5 Errors
This section documents warnings and errors generated by this task (if any). Note that warnings and
errors can also be generated in the SAS infrastructure libraries, in which case they would not be docu-
mented here. Refer to the index of all errors and warnings available in the HTML version of the SAS
documentation.
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DalError (error)
All errors from the dal resulting from an attempt to access a non-existing data set, table,
column, or attribute. This will usually hint at one or more invalid task parameter values.
NoOrPartialTemporalOverlap (error)
The time span covered by the object track data set objtrack does not or only partially
overlap with the exposure data in the input table table. This will usually hint at invalid
time boundaries that have been specied in running task iauephem.
6 Input Files
1. event list with sky image columns xcol/ycol generated by attcalc
2. data set generated by task iauephem dening the position of the moving object as a function
of time. Please note that iauephem does not have to be used to prepare the input but any
tools which generates a data set with a single binary table (with any name) and the folling
minimal column structure:
column name meaning type units
MJD modied Julian Day number real64 d
RA apparent geocentric Right Ascension real32 deg
DEC apparent geocentric Declination real32 deg
DELTA distance to center of earth real32 AU
7 Output Files
1. input event list with two columns xmovcol/ymovcol added
8 Comments
XMM-Newton is likely to observe various comets and other solar-system objects as part of the AO2
program. The proposed task shall be a valuable tool in the spatial analysis of the observation data
especially since the functionality does not seem to be readily available elsewhere.
9 Future developments
It is anticipated that more functionality shall be added to this package in the future. The proposed
task movecalc is an important part in the analysis of data from moving objects but can only address
spatial aspects. Another related task might be regionunmove to convert a spatial X MOV/Y MOV
region selection into X/Y space.
References
[1] E. W. Greisen and M. Calabretta. Representation of Celestial Coordinates in FITS. Astron. Astro-
phys., 1996. Found at the URL: ftp://fits.cv.nrao.edu/fits/documents/wcs/wcs.all.ps.
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