main

specsim.fitgalsim.main(args=None)

fitgalsim runs the galsim fiber acceptance calculation using class specsim.fiberloss.GalsimFiberlossCalculator and saves the mean and rms acceptance as a function of source profile (point source ‘POINT’, exponential ‘DISK’, De Vaucouleurs ‘BULGE’), effective PSF sigma (atmosphere+telescope blur), in um on focal surface, fiber offset from source on focal surface in um, and, for the extended source, the half light radius in arcsec.

The method consists in first setting sigma and offset grid, and reverse engineering the atmospheric seeing to retrieve the correct effective sigma on the grid given the telescope blur.

For each point in the output parameter grid (source type , sigma, offset, source radius), several calculations are done with random angular orientation of fiber and source to account for the fiber ellipticity (due to anisotropic plate scale) and source ellipticity.

The output file has to be saved in $DESIMODEL/data/throughput/galsim-fiber-acceptance.fits to be used for fast fiber acceptance computation. This idea is to compute accurate and correlated values of offset, blur, scale, atmospheric seeing from the fiber location and wavelength, compute the effective sigma and read with a ND interpolation the fiber acceptance value from the file.