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absseny stsdas.hst_calib.fos.y_calib



absseny -- Compute an FOS sensitivity curve.


absseny input wave mask startab table


This routine computes the FOS sensitivity by computing the ratio of an FOS observation to the actual stellar flux. The input FOS observation should have been calibrated by calfos, however, the FLX_CORR calibration step, i.e., the multiplication by the inverse sensitivity function, should be omitted. The actual stellar flux must be stored in a table having the columns WAVELENGTH and FLUX. Any of five methods can be used to match the wavelength scales of the observation and the actual stellar flux; methods are selected with the imode parameter.


input [file name]
Name of the image containing observed flux values.
wave [file name]
Name of the image containing wavelengths corresponding to the observed flux values. Wavelengths must be in ascending order.
mask [file name]
Name of the optional data quality mask image that specifies regions in the observed flux that are to be excluded.
startab [file name]
Name of the table containing the actual stellar flux. This table must have columns WAVELENGTH and FLUX---there can be no null values in either of the columns. The table must be sorted in ascending wavelength order.
table = "absseny" [file name]
Name of the output sensitivity table. This table will have the following columns:

     'WAVELENGTH' - Wavelength (real).
     'VALUE'      - Flux value (real).

The table will also have the header keywords DETECTOR, FGWA_ID, APER_ID, APER_POS, POLAR_ID, and PASS_ID.
(imode = 2) [integer, min=0, max=4]
Number specifying the interpolation or integration technique used to match wavelength scales. The following techniques---with their corresponding imode values---are available.

   IMODE                         METHOD
     0     Observed flux matched to actual flux wavelengths using
           linear interpolation.
     1     Actual flux matched to observed flux wavelengths using
           linear interpolation.
     2     Observed flux matched to actual flux wavelengths using
           trapezoidal integration.
     3     Actual flux matched to observed flux wavelengths using
           trapezoidal integration.
     4     Both actual flux values and observed flux values are
           integrated to equally spaced wavelength bins.   
(delw = 10.0) [real, min=0.1, max=200.0]
Wavelength bin size to use when imode = 4. This parameter is ignored for other values of imode.


1. Compute the sensitivity for a grating mode using an observation of a standard star with flux stored in a table called sstar. The observation file obs.c1h is in linearized count rates and its associated wavelength file is called wave.c0h. Output will be stored in a table named sens.

fo> absseny obs.c1h wave.c0h " " sstar sens 

2. Perform the prism calibration using observed flux values in the file pri_obs.c1h and wavelengths in the file pri_wave.c0h. Also use an input data mask pri_mask.cqh. Place the results in pri_sens. Set imode=3 for the prism because there may be large variations in the dispersion across the data.

fo> absseny pri_obs.c1h pri_wave.c0h pri_mask.cqh sstar pri_sens imode=3



Howard Bushouse, STSDAS


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