A general background or sky level (in photons per pixel) can be specified by the sky parameter. Background slope can be specified in photons per pixel in both the row and column directions by using the rowgrad and colgrad keywords. Slopes start at row=col=0.
The default image size is 64x64; larger (or smaller) images can be specified by the command line arguments nrow and ncol.
The random number generator can be started with different values by setting the seed to different integers. The default value is 1.
Two different forms of noise are simulated: The first is due to the statistical nature of photons. At each pixel the number of photons from the sky and the star are calculated. Then a random adu value picked from a Poisson distribution of that mean value is substituted. Secondly a a uniform noise value (like ccd read noise) specified by the rms keyword. Or Poisson noise can be generated by specifying the photon keyword.
The conversion from photons to analog to digital converter units can be made by setting the gain command line switch.
The command line parameters are recorded in the FITS header,including the location of star so that they can be extracted later.
pstar star=2800,10,22.4,5.3
Makes a 64x64 image in the file pstar.fts with an artificial star at (10, 22)
and a peak pixel count of 2800 photons. The image is `noise
free'
pstar star=2800,10,22.4,5.3 sky=10 star=1000,18,22,5.3
Does the same as the above but adds a background sky component, and a nearby
fainter companion with photon
noise.
pstar star=2800,10,22.4,5.3 photon
A field of stars can be generated by using the field command line argument.
You must specify the number of stars, the maximum integrated intensity in
counts, the minimum intensity in counts, and the fwhm. The program will
generate the requested number of stars with integrated intensities between
the maximum and minimum values randomly distributed in a logarithmic
manner and distributed randomly about the image. The program prints out a
list similar to that put out by stars of the coordinates. The coordinates can
also be found in the FITS
header.
A rectangular grid of stars can be generated using the grid option which is similar to the field except that they are regularly spaced and diminishing intensity along the rows.
The rand() function used to generate the random numbers is system supplied and has poor spectral properties so deficiencies in the generator may appear in some studies.
The photon noise feature is very slow.