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bspec -- Compute FOS scattered light spectrum
bspec spectab scattab detector grating
This task performs theoretical modeling only. It is NOT an absolutely calibrated reduction tool. Accuracies are limited by the completeness of the treatment of the basic optical principles employed, the correctness of the optical specifications of the FOS, and the input template spectra. This task is intended for use as a post-observation parametric analysis tool only.
For a given input spectrum the bspec task computes the scattered light spectrum that is produced by a specified observing mode of the FOS. The input spectral data must be in STSDAS table format and must contain columns of wavelength and flux values. The wavelength data must be in units of Angstroms and the flux data in units of counts per second per pixel. Furthermore, the input spectral data must already be convolved with the throughput functions of all the FOS optical components EXCEPT that of the grating blaze function. The task countspec can be used to produce such a countrate spectrum from calibrated spectral data for any source. The input spectral data should extend to a maximum wavelength of at least 6000 Angstroms in order to insure reliable modelling of scattered red light.
The output of this task is an STSDAS table containing several columns of spectral information. Those columns of most interest to the user are "gwav" (wavelength) and "ablg" (total intrinsic+scattered light countrate spectrum). These data can be easily plotted using the task sgraph, for example. The output table columns are:
angle - array of diffracted angles (degrees) blg - array of intensity due to blazed grating only apd - array of intensity due to finite aperture (LSF) ablg - array of intensity due to blazed grating + aperture benv - input spectrum dispersed with grating equation bfu - grating blaze function (of selected order) gwav - wavelengths corresponding to diffracted angles
Note that the "benv" data column contains the dispersed light spectrum only, while the "ablg" data column contains the spectrum of dispersed and scattered light, hence the difference ("ablg-benv") corresponds to the scattered light spectrum only.
- spectab [file name]
- Input spectrum table name. Must contain two columns of data labeled "wavelength" and "flux", with the wavelengths in units of Angstroms and the flux data in units of counts per second per pixel.
- scattab [file name]
- Output spectrum table name.
- detector [string, allowed values: red | blue]
- FOS detector name.
- grating [string, values: g130h|g190h|g270h|g400h|g570h|g780h|g160l|g650l]
- FOS grating name. The combination of detector and grating names is used by the task to select the proper set of grating parameters to be used in the modelling. Note that the two detector/grating combinations "red/g130h" and "blue/g780h" are not allowed.
- (instpars = "") [pset]
- Parameter set containing the grating parameters. A null value causes the task to automatically select the appropriate parameters for the specified detector and grating.
- (low_ord = 1) [integer]
- Lowest order to be included in calculations.
- (high_ord = 5) [integer]
- Highest order to be included in calculations. For extremely red stars it may be useful to set this parameter to as high as 10.
- (glsf = 0.003) [real]
- The e-folding length (in diodes) of the wings of the Voigt LSF.
- (slsf = 0.01) [real]
- The core width (in diodes) of the Voigt LSF.
- (flat = 1.5E-6) [real]
- The level of the flat (baseline) component of the Voigt LSF.
- (lmin = 0) [real]
- Lower limit of the wavelength range to be included in the calculations. If lmin is less than the limit of the input spectrum, the min wavelength of the input spectrum will be used.
- (lmax = INDEF) [real]
- Upper limit of the wavelength range to be included in the calculations. If lmax is greater than the limit of the input spectrum, the max wavelength of the input spectrum will be used.
- (iop = 0) [integer, min=0, max=4]
- Operation code: 0 - evaluate and convolve grating and LSF characteristics; 1 - evaluate grating only; 2 - evaluate grating and aperture LSF; 3 - convolve grating and aperture LSF characteristics; 4 - evaluate grating blaze function for order "low_ord".
1. Compute the scattered light spectrum for a G2V star spectrum (produced using the countspec task) for the FOS blue-side and grating g190h. The input spectrum is in the table "fos_g2v_spec.tab" and the results will be stored in the table "scatter.tab". Plot the results using sgraph.
te> bspec fos_g2v_spec scatter blue g190h te> sgraph "scatter gwav ablg" logy+ te> sgraph "scatter gwav benv" logy+ append+
Two instrument science reports which describe the practical usage of this task are: FOS ISRs 127 and 150.
This task was originally written by M.R.Rosa and TH.Mueller at ST-ECF and was ported to the IRAF/STSDAS environment by H.Bushouse (STScI).
For assistance using this or any other tasks, please contact firstname.lastname@example.org or call the help desk at 410-338-1082.