Several RegriddedFrames created from ReducedScienceFrames (see the http://www.astro-wise.org/portal/howtos/man_howto_reduce/man_howto_reduce.shtmlReduceTask HOW-TO or the http://www.astro-wise.org/portal/howtos/man_howto_regrid/man_howto_regrid.shtmlRegridTask HOW-TO) can be coadded to form a deeper image with a substantial reduction of chip defects and divisions (a CoaddedRegriddedFrame).
NOTE: At this time, the CoaddTask does not allow frames from multiple instruments to be coadded. It should be possible to do this provided all the RegriddedFrames were regridded to the same grid target (R.A., DEC., and pixel scale1), but this operation is currently not supported.
At the moment, the CoaddTask is a purely serial operation which takes place on only one node of the DPU. Some possible reasons to use the DPU for this task are because the machines on the DPU are much faster than the local machine, or because no local machine is available.
For the CoaddTask, the DPU command would look something like:
awe> dpu.run('Coadd', d='2000-01-01', i='WFI', f='#843', o='Science1_?-*')
The CoaddTask options via the DPU are as follows:
This example shows how to run the DPU CoaddTask using date, filter, and object information. This allows one to process all data for a given object on a specific day taken in a certain filter, for all CCDs of the mosaic.
The options can be used in any order and can be omitted (except `i'), but the likelihood of locating required data depends on relaying a minimum of information as shown in the examples.
This task can also be performed in on a per chip basis. The CoaddTask is main part of the recipe $AWEPIPE/astro/recipes/Coadd.py. This is most basic front-end for creating CoaddedRegriddedFrames in AWE. An examples of the syntax for the CoaddTask is given below:
awe> coa = CoaddTask(instrument='WFI', date='2000-01-01', chip='ccd50', ... filter='#843', object='Science1_?-*') awe> coa.execute()
The CoaddTask options are as follows:
This example shows how to run the CoaddTask using date, chip, filter, and object information. This allows one to process all data for a given object on a specific day taken in a certain filter, and only one CCD of the mosaic.
The options can be used in any order and can be omitted, but the likelihood of locating required data depends on relaying a minimum of information as shown in the examples.
The algorithm behind the coaddition is described via the coaddition of two RegriddedFrames which have
the (object)name reg1 and reg2.
The value fout
where the summation is over the RegriddedFrames.
The relation between pixel units in CoaddedRegriddedFrame and the RegriddedFrames from which it was derived is as follows.
For a RegriddedFrame object named reg
At magnitude=0 pixels will have counts
countsreg(mag = 0)
(Note that reg.ZEROPNT is exposure-time specific, therefore counts instead of countrate.)
Suppose one makes a CoaddedRegriddedFrame from this single RegriddedFrame reg
Suppose you know the physical flux density of the magnitude=0 object to be f0
For example, in the AB magnitude system f0 = = 3631
If ones make a CoaddedRegriddedFrame out of multiple overlapping RegriddedFrames the resulting flux is the weighted average of the input RegriddedFrames fluxes (see Section ).
fout = 1#1(wi*FLXSCALEi*fi)/1#1(wi),
(1.1)
FLXSCALEi
wi = weighti/FLXSCALEi2
The fi
The value wout
wout = 1#1(wi)
(1.2)
1.1.4 Coadd units
The pixel units of the CoaddedRegriddedFrame are fluxes relative to the flux corresponding to magnitude=0.
In other words, the magnitude m
m = - 2.5log10f0.
(1.3)
reg.FLXSCALE = = 10.0-0.4 x reg.ZEROPNT
(1.4)
countsreg(mag = 0) = = 100.4 x reg.ZEROPNT = 1/reg.FLXSCALE
(1.5)
vcoad = countsreg*reg.FLXSCALE
(1.6)
fcoad(Jy) = f0*vcoad
(1.7)
fcoad(Jy) = 3631*vcoad
(1.8) Footnotes