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Дата изменения: Tue Aug 16 06:20:10 2005
Дата индексирования: Tue Oct 2 03:04:08 2012
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XMM-Newton Science Analysis System Page: 1
omgprep
August 16, 2005
Abstract
The task omgprep prepares the OM grism image for detection and extraction of
spectra (introduces distortion corrections, properly rotates the image, etc.)
1 Instruments/Modes
Instrument Mode
OM IMAGING
2 Use
pipeline processing yes
interactive analysis yes
3 Description
This tasks clones the OM Imaging Mode Data Image File with the Grism-1 or Grism-2 lter for subsequent
pipeline processing. The image le is prepared for extraction of spectra produced by grisms: rst the
distortion correction is applied, then the image is rotated by the angle corresponding to the grism lter
in order to align spectra with respect to the pixel columns (for optimisation of spectra extraction)
Values for additional FITS header keywords necessary for the creation of SSC Data products by sub-
sequent pipeline tasks are taken directly from the OM Priority Window Data Auxiliary File, the OM
Periodic and Non-Periodic Housekeeping Files and from the OM Observation Summary File through the
ODF Access Layer(OAL) and stored in the Primary Header of the output les.
The task rst reads the binning factors (BINAX1 and BINAX2) from the FITS header, along with the
BPE binning ag (BINBPE) and the x and y size of the OSW window (in centroided pixels) along with
the x and y o sets of the window. The pixel coordinates of the OSW source list are then converted to
the PIXCOORD reference frame (2048 by 2048 centroided pixels).
The OM optics have a small amount of distortion, and the CAL call omDistortion is used to get the
o sets of the pixel position from a linear scale. These o sets are then applied to the pixel positions. A
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call to GetPlateScale (CAL) is subsequently used to convert from pixels to radians. The center of the
detector, i.e. the position of the OM boresight is pixel 1023.5, 1023.5.
The shift and add process is all performed relative to a reference frame (used to nd the tracking stars), so
a call to OAL getAttitude is used, with the time of the reference exposure, to get the spacecraft attitude.
The CAL Boresight routine is used to obtain the boresight o set matrix, which is applied to the s/c
attitude to get the OM boresight direction. The nal section of the code takes the OM OSW image and
rotates it in order to align the spectra with respect to the pixel columns.
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
set yes string none
Input OM image lename (output from ommodmap)
ppsoswset yes string none
PPS OM OSW FITS output image lename
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.
di Bin (fatal)
Di erent binning in x and y directions
RA of OM boresight (warning)
corrective action: Information about the Right Ascention of the OM boresight
DECL of OM boresight (warning)
corrective action: Information about the Declination of the OM boresight
DETSEC keyword missing (warning)
corrective action: Issue a warning about the missing keyword in the input le. DETSEC
keyword for output le is not inserted
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6 Input Files
1. OM OSW FITS image (as produced by ommodmap)
7 Output Files
1. PPS OM OSW FITS image with spectra aligned with the pixel columns.
8 Algorithm
subroutine omgprep
open output file
read the OSW window parameters, binning factors from header
call CAL_GetBoresightMat
call OAL_GetAttitude (with time of reference frame)
find OM boresight direction
undistort image
rotate by the angle corresponding to the grism filter
write out to a fits file.
close OSWSL
close output file
end subroutine omgprep
9 Comments
 none
10 Future developments
Currently the standard CAL procedure for distortion correction is implemented. On the availability of
new calibration data related to the additional distortion introduced by the grism lters the distortion
correction will be improved.
References
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