SALT/PFIS VPH Spectroscopy Simulator

• Choose a VPH grating
• Enter either a central wavelength or a grating angle
  • The camera angle will be assumed to be twice the grating angle.
  • Angles greater than 50 are not allowed, angles below 10 degrees are not practical due to zeroth order contamination.
  • The grating angle will be quantized by 0.375 degree increments
• The following information will be produced:
  • Wavelength limits on the detector
  • Wavelengths that fall in the detector gaps
  • Spectral resolving power (at the central wavelength) for the given slit width
  • Slit throughput for given slit width and zenith seeing (0.9 arcsec is the median seeing at the SALT site).
• The slit width and zenith seeing may both be adjusted to determine changes in the resolving power and slit throughput, with the following caveats:
  • The resolving power assumes a filled slit (resolution will be better for point sources)
  • The slit throughput assumes a Gaussian seeing function (use of an actual seeing function would reduce this number by about 10%) as well as factors in 0.6 arcseconds of image degradation by the telescope and SAC optics
• All information is for on-axis sources. However, plots are available that show the change in efficiency and wavelength coverage for sources that are off-axis in the dispersion direction. These are necessary for determining efficiencies for multi-object spectroscopic observations.