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deaccum stsdas.hst_calib.fos



deaccum -- Unstack ACCUM mode FOS images.


deaccum input output


The deaccum task "unstacks" the accumulated data contained in each group of an FOS ACCUM-mode multigroup image. For an ACCUM-mode image the data contained in image group "n" represents the accumulation of all data from groups 1 through n. This task recursively subtracts the data in group "n-1" from that in group "n", so that what remains is the data that was accumulated during the exposure time for group "n" only.

For raw (e.g. d0h) data files the data in group "n" is the total of all counts received for groups 1 through "n" and therefore the "deaccum" process simply subtracts the data in group "n-1" from that in group "n". For calibrated data files, i.e. any data files where the data have been divided by the exposure time (e.g. c4h data in counts per second or c1h data in ergs per second), the flux data contained in group "n" is the average of groups 1 through "n". Therefore these files are "deaccum'ed" by first scaling the data in each group by the total exposure time for that group, subtracting the scaled data in group "n-1" from group "n", and finally dividing the data in each group by the individual group exposure times.

This task will only work for data files that contain "flux" data, i.e. only data files that contain pixel values representing source intensity or fluxes. It will also work with statistical error (c2h) files and correctly "deaccum's" these data in quadrature. This task will NOT work for data files that contain wavelengths (c0h) or data quality values (q0h or cqh files).

The group parameter "EXPOSURE" is updated in the output image headers to reflect the change in exposure time associated with each data group.


input [file name template]
Input image name or list.
output [file name template]
Output image name or list. The number of input and output images must the same.
(verbose = yes) [boolean]
Print operations as they are performed?


1. Unstack the calibrated flux data in the image y0xi0203t.c1h, writing the results to the new image y0xi0203u.c1h.

	fo> deaccum y0xi0203t.c1h y0xi0203u.c1h

2. Unstack the flux data in image y15i0206t.c1h and the error data in image y15i0206t.c2h into the new images y15i0206x.c1h and y15i0206x.c2h.

	fo> deaccum y15i0206t.c1h,y15i0206t.c2h y15i0206x.c1h,y15i0206x.c2h



Author: Howard Bushouse, STSDAS


For assistance using this or any other tasks, please contact or call the help desk at 410-338-1082.


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