abssenz

abssenz

stsdas.hst_calib.hrs.z_calib

abssenz

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

NAME

abssenz - Compute the absolute sensitivity ratio.

The absolute sensitivity ratio for a single grating mode is computed by taking the ratio of the observed flux values in the table input and the actual flux values for the standard source spectrum in the table standard. The resulting ratio is placed in the table output.

ALGORITHM

The core of this task is a simple division of the spectrum found in the input table by the standard star spectrum found in the standard table.

To match resolutions between the observation and standard spectra, the standard spectrum is integrated. Specifically, each row in the input table defines a flux value and a range of wavelengths represented by that flux value. The standard is rebinned by integrating the standard between the low and high wavelength for the corresponding point in the input table. Standard trapezoidal integration is used. This produces a standard spectrum having the same resolution as the input spectrum.

If error columns are found in either or both the input and standard tables, an error column is produced in the output table, propogating the input errors.

INPUT TABLE

The input table will have the following columns. The column names are defined in the cfcolnames pset. The names below are the default column names. This table is produced by the tasks centerflux and mergecar. The ERROR column is not necessary. If present, abssenz will propogate the error and place the results in the output table. However, if not present, no error propogation will occur (unless the standard star table has an error column).

	'FLUX'   - Average count rate over the 
		   specified wavelength range.
	'WLOW'   - First wavelength in the range averaged.
	'WHIGH'  - Last wavelength in the range averaged.
	'ERROR'  - The standard deviation of the mean.

The following columns are optional and, if present, are copied to the output table. The information in them is not used in abssenz.

	'CARPOS' - Carrousel position.
	'ORDER'  - Spectral order, ("1" for first order
        	   gratings).

The following header parameters are also copied to the output table. abssenz does not use these values for any calculations.

	'GRATING'  - The grating represented by the contents of the
		     table.
	'APERTURE' - The aperture represented by the contents of the
		     table.

STANDARD TABLE

The standard star table contains the following columns. The ERROR column is not necessary. If present, abssenz will propogate the error and place the results in the output table.

	'FLUX'	     - Flux for the spectrum.
	'WAVELENGTH' - Wavelength of the flux.
	'ERROR'      - Error in the flux.

OUTPUT TABLE

The output table will contain the following columns.

	'VALUE'      - The ratio of the observation to standard.
	'WAVELENGTH' - The wavelength of the ratio.

If either the input observation table or standard star table contained error information, that error will be propogated by abssenz and placed in the following column:

	'ERROR' - Error in the ratio value.

The following columns are copies of the corresponding columns in the input observation table.

	'CARPOS' - Carrousel position.
	'ORDER'  - Spectral order, (1 for first order
        	   gratings).

The following header parameters are also copied from the input table. abssenz does not use these values for any calculations.

	'GRATING'  - The grating represented by the contents of the
		     table.
	'APERTURE' - The aperture represetned by the contents of the
		     table.

PARAMETERS

input [file name]: Input flux table created by the tasks centerflux or mergecar.

standard [file name]: Standard stellar flux table for the observed object.

output [file name]: File name for the output ratio table.

(cfcolnames = "") [pset]

The parameters that define the column names in the output table. The parameters are:

(carpos = "carpos") [string]: Name of the column containing carrousel positions.

(order = "order") [string]: Name of the column containing the spectral orders.

(wlow = "wlow") [string]: The name of the column containing the low wavelength of the regions averaged together.

(whigh = "whigh") [string]: The name of the column containing the high wavelength of the regions averaged together.

(flux = "flux") [string]: The name of the column containing the average flux.

(err = "error") [string]: Name of the column containing the standard deviations of the means.

(npts = "npts") [string]: Name of the column containing the number of pixels included in the average calculation.

(spcolnames = "") [pset]

This pset contains the parameters that define what columns should be found in the standard star table. If blank, then no column containing the corresponding data will be looked for. The parameters are:

(flux = "flux") [string]: The name of the column containing then standard star flux.

(err = "error") [string]: Name of the column containing the associated error in the flux.

(wavelength = "wavelength" [string]: Name of the column containing the associated wavelength of the flux.

(racolnames = "") [string]

This pset contains the parameters that define the column names in the output table containing the ratio. If blank, the column containing the corresponding data will not be created. The parameters are:

(carpos = "carpos") [string]: Name of the column containing carrousel positions.

(order = "order") [string]: Name of the column containing the spectral orders.

(value = "value") [string]: Name of the column containing the sensitivity ratio.

(wave = "wavelength" [string]: Name of the column containing the associated wavelength of the flux.

(err = "error") [string]: Name of the column containing the associated error in the flux.

EXAMPLES

1. Calculate the center fluxes for all the observations in the current directory. Then calculate the sensitivity ratio using the standard "standard.tab".

	cl> centerflux *.c1h fluxtab
	cl> abssenz fluxtab standard ratio