STScI Logo

cathodemap stsdas.hst_calib.hrs.z_calib



cathodemap -- Compute the granularity of the GHRS photocathode.


cathodemap input avefile smoothfile cathodemap


Using observations of standard stars at about the same photocathode line position, the photocathode granularity is computed by summing the observations on a uniform sample scale and removing low frequency variations across the photocathode (by dividing the sum by the data), after smoothing. Data is smoothed by fitting a least squares cubic spline with an adjustable number of nodes through the data.

The input observations for this routine should be taken with comb-addition. On-board Doppler compensation should not be used since it may smooth the granularity. The data should be quarter-stepped.

The data must be calibrated with calhrs and the following calibration steps must be performed before using the data as input to cathodemap:

     1) Removal of diode non-linearities and non-uniformities (DIO_CORR).
     3) Computing the photocathode mapping function (MAP_CORR).
     2) Merging of the substep bins (MER_CORR).


input [file name template]
Template of the input quarter-stepped stellar observations with the mapping function previously computed and corrected for diode non-uniformities and non-linearities .
avefile = "avefile" [file name]
Name of the output file to contain a image of the averaged counts for all input observations resampled on a quarter stepped (sample spacing=0.25) scale starting at sample 0.
smoothfile = "smoothfile" [file name]
Name of the output image containing the least squares cubic spline fit through the data in avefile.
cathodemap = "cathodemap" [file name]
Name of the output image containing the cathode granularity.
(nodes = 15) [integer, min=3, max=30]
Number of equally spaced nodes in the least squares cubic spline.
(niter = 10) [integer, min=1, max=INDEF]
Number of iterations of the Levenberg-Marquardt non-linear least squares algorithm used to fit the spline curve.
(template = "hrs$templates/hrsphc") [input file name]
Name of the template file used to construct the output cathodemap file.


1. Compute the granularity using the input data files, obs1, obs2, and obs3. Place the results in files ave, smoothed, and granularity.

hr> cathodemap obs1.hhh,obs2.hhh,obs3.hhh ave smoothed granularity 




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


Source Code · Search Form · STSDAS