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absfitz stsdas.hst_calib.hrs.z_calib


NAME · USAGE · DESCRIPTION · PARAMETERS · EXAMPLES_ · BUGS
REFERENCES · HELP · SEE_ALSO

NAME

absfitz -- Generate a smooth sensitivity curve.

USAGE

absfitz table wave sens

DESCRIPTION

This routine generates a smooth curve through the sensitivities in an input ratio table that was previously generated by the abssenz task. The curve is the least squares cubic spline with a specified number of equally spaced nodes, or a table of unequally spaced nodes. The least squares fit is done using the Levenberg-Marquardt Method. If the number of input nodes is set to zero, then no fit is done and the output sensitivity curve will be the cubic spline passing through all input data points.

The smoothed output sensitivity curve (for use by the Routine Science Data Processing (RSDP) system), is generated with equally spaced wavelengths specified by the delw parameter in the range wfirst to wlast. If delw = 0.0, then the sensitivity curve will be generated at the wavelengths taken from the input sensitivity table.

This routine must be called twice for each grating in order to generate the files needed by RSDP. The first call places the small science aperture calibration in the first group of the output files and the second call places the results for the large science aperture in the second group of the output files.

PARAMETERS

table [file name]
Name of the input ratio table containing the raw sensitivity values. The following table columns are needed:

	'WAVELENGTH' - Wavelengths (double).
	'VALUES'     - Raw sensitivity values (double).

This table is generated by the abssenz task---table rows are sorted by ascending wavelength order. (The tsort task can be used to sort any unsorted tables).

wave = "abswave" [file name]
Name of the output wavelength image that will be used by RSDP.
sens = "abssens" [file name]
Name of the output sensitivity image that will be used by RSDP.
(innodes = " ") [file name]
Name of the input table containing node positions. This table is specified only when nodes are unequally spaced. The innodes table will have between 2 and 20 rows--the node position will be in the WAVELENGTH column. If no table name is specified for innodes, then this task assumes that equally spaced nodes are desired, and the user must specify the number of nodes using the nodes parameter.
(outnodes = "nodes.tab") [file name]
Name of the output table to contain the wavelengths and fitted sensitivities at the cubic spline nodes. This table has the following columns:

	'WAVELENGTH' - Wavelength for the node (double).
	'VALUE'      - Sensitivity value at the node (double).
(numnodes = 10) [integer, min=0, max=20]
Number of equally spaced nodes in the least squares cubic spline fit. This parameter is used only if no file name is passed to the innodes parameter. If nodes is set to 0, then no fit will be done and the output sensitivity will be the cubic spline through all input ratios.
(delw = 0.0) [real, min=0.0, max=500.0]
The wavelength spacing for generating the output sensitivity curve. If delw is set to 0.0 then the output wavelengths will be taken from the WAVELENGTH column of the input raw sensitivity table (i.e., it will come from table).
(wfirst = 0.0) [real]
The starting wavelength in the output sensitivity image. If delw = 0.0 then this parameter is ignored. If wfirst = 0.0 then the first wavelength in the input sensitivity table is used.
(wlast = 0.0)
The ending wavelength in the output sensitivity image. If delw = 0.0 then this parameter is ignored. If wlast = 0.0 then the last wavelength in the input sensitivity table is used.
(niter=10) [integer, min=1, max=100]
The number of iterations of the Levenberg-Marquardt least squares algorithm that are to be performed. Under normal circumstances 10 iterations should be more than sufficient.
(wtemplate = "hrs$templates/hrsnet.hhh") [file name]
Name of the template header for the output wavelength file. This template defines the non-standard group parameter structure.
(stemplate = "hrs$templates/hrsabs.hhh) [file name]
Name of the template header for the output sensitivity file. This template defines the non-standard group parameter structure.

EXAMPLES

1. Compute sensitivity curves using the input tables g2ssa.tab and g2lsa.tab (previously created with abssensz). Use the default value of 15 equally spaced nodes. Place the output wavelength and sensitivities in files named g2wave and g2sens, respectively. The first task run will generate results for the small science aperture, the second for the large science aperture. Both input tables g2ssa and g2lsa must have the same number of rows.

	hr> absfitz g2ssa g2wave[1/2] g2sens[1/2]
	hr> absfitz g2lsa g2wave[2] g2sens[2]

2. Repeat the process, this time using unequally spaced node positions in the WAVLENGTH column of table g2nodes.tab. Generate output sensitivity images with a wavelength spacing of 5 Angstroms from 1000 to 2300 Angstroms. In this case, g2ssa and g2lsa are not required to have the same number of rows.

	hr> absfitz.innodes = g2nodes
	hr> absfitz.delw = 5.0
	hr> absfitz.wfirst = 1000.0
	hr> absfitz.wlast  = 2300.0
	hr> absfitz g2ssa g2wave[1/2] g2sens[1/2]
	hr> absfitz g2lsa g2wave[2] g2sens[2]

3. Generate a sensitivity curve for the input table rawsens.tab. Do not perform a least squares fit--simply generate a cubic spline going through all points in rawsens from 2000 to 3000 with a spacing of 1.0 Angstrom.

	hr> absfitz rawsens wave sens wfirst=1000 \
		wlast=2000 delw=1.0

BUGS

Unpredictable results will occur if multiple group output files are constructed with different numbers of points in each group.

REFERENCES

HELP

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

SEE ALSO

abssensz, centerflux, mergecar


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