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dopoff -- Determine Doppler compensation magnitude for GHRS data.
This task calculates the magnitude of the Doppler compensation for Goddard High Resolution Spectrograph (GHRS) data. The values are used by the specalign task as a measure of the granularity shift (see the help for specalign for more information).
Input for this task is a table (normally produced by the poffsets task) that contains a list of file names used by the specalign task for combining spectral data. dopoff adds a column---specified by the gran_col parameter---containing Doppler compensation magnitudes for the data. This name of this column is later used when running the specalign task, and consequently, is the input value for the goff_col parameter of specalign.
The table should have two columns defined:
'file_col' - Names of the data files. 'group_col' - Group numbers for data in corresponding files.
Also as input, the task assumes that the ULH files exist; it will construct the ULH file names by changing the extension of the input files from the file_col file to ".ulh".
Output is written to the column specified by the gran_col parameter. If the column does not exist, it is created. If the column already exists, two options are available:
'overwrite = yes' - If the column exists, existing values are overwritten. 'overwrite = no' - If the column exists, an error message is displayed.
Values written to the gran_col are the relative Doppler compensation values. The values are determined as:
offset = doppler(current) - doppler(reference)
The reference data is specified in the parameter reference. If the parameter is blank, the first file from the input table is used as the reference.
- input [file name]
- Name of the input table containing the file names and group numbers of the data for which Doppler compensation magnitudes will be determined.
- (reference = "") [file name]
- Name of the reference data file for which the Doppler compensation will be computed. If not specified, the first file from the input table will be used as the reference. The column is then filled with the relative Doppler compensation shifts.
- (gran_col = "goff") [string]
- Name of the column to create or overwrite with the calculated Doppler compensation offsets.
- (file_col = "file") [string]
- Name of the column that contains the data file names.
- (group_col = "group") [string]
- Name of the column that contains the group numbers for the corresponding data files.
- (overwrite = no) [boolean]
- Overwrite any existing values in the gran_col column?
If this is set to "no" and the column specified by the parameter gran_col exists, the program will abort. If "yes" is specified, then the contents of the column will be overwritten.
1. Determine the Doppler compensation offsets for the observation z1x23456m.
cl> poffsets z1x23456m shift.tab cl> dopoff shift.tab
The document describing the GHRS is "SI Systems Description and User's Handbook for the High Resolution Spectrograph (HRS) for the Hubble Space Telescope (HST)", Ball Aerospace, SE-01.
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