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omgrism
June 28, 2006
Abstract
Extracts source spectra from OM Grism OSW image FITS les.
1 Instruments/Modes
Instrument Mode
OM IMAGING
2 Use
pipeline processing yes
interactive analysis yes
3 Description
This task constructs the PPS product, grism spectra, extracted from an Optical Monitor image obtained
with one of the OM grism-lters. The image is previously undistorted by omgprep and rotated in order
to align the spectra with the image columns. The task makes use of a source-list produced by running
omdetect on the same image. The output le contains tables with background subtracted spectrum rates
& corresponding errors, background rates & error, spectrum ux & error. All rates are in counts=s=  A,
and the uxes are in ergs=s=cm 2 /  A.
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
set yes string
OM image le with grism spectra aligned with respect to the columns of the image (output from omg-
prep).
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sourcelistset yes string
Source list (output from omdetect)
outset yes string
Output spectra le
regionle no string
Name of the ASCII (input) region le
spectraregionle no string
Name of the ASCII (output) spectra region le
outspectralistset no string
Output le containing the extracted spectra list (in a brief form)
extracteldspectra no logical false
If set to true switches the task into the mode for extraction of all available spectra in the eld
spectrumhalfwidth no real -8. -20 to 20
Halfwidth of the spectrum extraction region; expressed in pixel, if negative, or in FWHWs, if positive
bkgosetleft no real 0. -20 to 20
Oset of the left background extraction region (from the left edge of the spectrum extraction region); in
pixels, if negative, or in FWHWs otherwise.
bkgwidthleft no real -8. -40 to 40
Width of the left background extraction region; in pixels, if negative, or in FWHWs otherwise.
bkgosetright no real 0. -20 to 20
Oset for the right background extraction region (from the right edge of the spectrum extraction region);
in pixels, if negative, and in FWHWs otherwise.
bkgwidthright no real -8. -40 to 40
Width of the right background extraction region; in pixels, if negative, or in FWHWs otherwise.
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spectrumsmoothlength no integer 0  0
Length of the smoothing window for smoothing the output spectra (if smoothing is desirable); the pa-
rameter set to 0 or 1 implies no smoothing.
extractionmode no integer 0 extractionmode  0
Switch between dierent extraction modes. The value 0 corresponds to the normal extraction (summation
of counts in the cross-dispersion direction); 1 corresponds to the Optimal Extraction (Horne's algorithm);
2 corresponds to the one-dimensional spline smoothing (in the cross-dispersion direction); 3 corresponds
to the one-dimensional Gaussian t (in the cross-dispersion direction).
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.
The spectrum is badly aected by Mod-8 noise / coincidence loss (warning)
corrective action: Issue a warning.
Could not nd any compatible blocks in set (warning)
corrective action: The input source list le is empty (probably no sources were detected by
omdetect. Issue a warning. No spectra will be extracted
6 Input Files
1. OM grism, rotated image le (output from omgprep)
2. OM source list le (output from omdetect)
7 Output Files
1. PPS product OM OSW FITS spectra
2. FITS le containing the list of all the extracted spectra (by request, using the outspectralist
parameter
3. ASCII le containing the extracted spectra regions
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8 Algorithm
subroutine omgrism
read parameters
get handle on source rates file
check if this file contains data
get handle on the input image file
check if the image file corersponds to the Grism-1 or Grism-2 filters
set the grism-state for the CAL routines
get CAL plate scale
get the number of sources detected by omdetect
allocate indicators for source shapes and source relations
loop source=0, nSources
determine the source shape and classify each source
according to the filter-dependents specific criteria
end loop
loop source=0, nSources
if source is extended (first-order)
loop iSource=0, nSources
check if the extended source corresponds to a
point-like source (zero-order) by the criteria
corresponding to the given Grism filter
and mark the zero- and first-order sources as
related to each other
end loop
end if
end loop
loop source=0, nSource
if source is marked as having a corresponding zero-order
within the image then extract the spectrum and add
the corresponding data table to the output FITS-file
end loop
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write spectra keywords to header
write output spectrum file
release handles
end subroutine omgrism
9 Comments
The optimal extraction algorithm for spectra extraction is under development.
10 Future developments
 Spectra extraction algorithms to be improved
 Coincidence-loss correction to be applied
References
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