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omregion
July 2, 2008
Abstract
Calculates evselect region les for an OM source
1 Instruments/Modes
Instrument Mode
OM FAST
2 Use
pipeline processing yes
interactive analysis yes
3 Description
This task takes an OM OSW source list and a source number and produces evselect region les for the
source and its associated background.
The source extraction region is a circle, centred on the source position and extending out to srcrad (default
3) times the FWHM of the source PSF (as given in the source list). The background extraction region
is normally an annulus with the inner radius of backinner times the source extraction radius (default 1),
and the outer boundary dened by backouter times the source extraction radius (default 2).
If the nearest neighbour is within srcrad FWHM of the source extraction circle, then the source extraction
circle is reduced in size until the extraction region is no longer contaminated. A warning is issued in this
case.
If a source is within srcrad FWHM of the background extraction annulus then a circle of srcrad FWHM
surrounding this source is excluded from the background region.
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4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
set yes string
The input OM OSW source list
srcnumber yes integer
The number of the source in the OM OSW source list
srcradius yes real 3
The size of the source extraction radius: in FWHM of the source PSF, if it is positive, and in xed pixels
if it is negative
bkginner yes real 1
The inner radius of the background extraction region in terms of the source region radius
bkgouter yes real 2
The outer radius of the background extraction region in terms of the source region radius
nfwhm yes real 3
The limiting source extent in terms of the PSF FWHM
srcle yes string
The name of the source extraction region le
bkgle yes string
The name of the background extraction region le
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
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documentation.
The source number exceeds the number of sources in the OSW (fatal)
6 Input Files
1. PPS product OM OSW source list (produced by omdetect or omwavelet)
7 Output Files
1. Intermediate source region le for use by evselect
2. Intermediate background region le for use by evselect
8 Algorithm
subroutine omregion
read in source list
if (srcnumber > number of sources in list) issue fatal error
locate the srcNumber'th source
x = XPOS
y = YPOS
fwhm = FHWM ! obtained from source list rather than the CAL
r1 = fwhm * srcRadius
nearest = 1.e30
loop over all sources except the selected source
if (distance to this source < nearest) then
nearest = distance to this source
size = fwhm of this source
endif
endloop
if (r1 > (nearest - nfwhm * size)) then
r1 = nearest - nfwhm * size
warn that the size of the extraction region is begin reduced
if (r1 < 0) then
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warn that the source is unavoidably contaminated
r1 = fwhm
endif
rInner = r1 * bkgInner
rOuter = r1 * bkgOuter
ncontaminating = 0
loop over all other sources
compute distance to source dist
if (rInner < (dist - nfwhm * fwhm of this source) < rOuter) then
store contaminating source x, y, fwhm
ncontaminating++
end loop
open source region file
write out source region file
close source region file
open background region file
write out background annulus
loop over ncontaminating sources
write out exclusion circle for this source
end loop
close background region file
end subroutine omregion
9 Comments
10 Future developments
 Could use a more sophisticated method for the contamination searches, perhaps based on
source ux ratios and errors
 Could have a list of source numbers as input and output a set of region les based on those
sources. The output region les could be based on the input root plus the source number.
The problem with this is that it would contradict the pipeline philosophy of always specifying
all input and output parameters.
 omdetect and omwavelet will produce source lists with ellipsiodal shapes for objects. This
task should be able to produce ellipses and elliptical annulli for the extraction regions.
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References
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