FOCSIM is a menu driven interactive FORTRAN program which runs under IRAF. It accepts user input describing the FOC observing configuration and the physical characteristics of an astronomical source to be observed. The user may select from a number of model spectra, have FOCSIM create its own synthetic spectrum (black-body, power law or flat), or use his own file of wavelengths and fluxes in appropriate units. The sources resident in the program include 77 simulated stellar spectra covering a wide range of MK classes generated by the Kurucz (1979) stellar atmosphere models and a number of UV standard stellar spectra from IUE (Ap. J. Suppl., 40, 1, 1979). In addition, FOCSIM can create its own flat continuum between two wavelengths, line spectrum with up to three emission lines, blackbody source of arbitrary temperature or power low spectrum of arbitrary index. The normalization factors of flux and wavelength can all be specified arbitrarily by the user. Furthermore, the diffuse background can also be calculated precisely by FOCSIM using zodiacal light spectrum for UV air glow and the inherent detector background can be accommodated with user supplied intensities. Unfortunately, FOCSIM currently only simulates the normal 512 x 512 imaging format. When using different formats, the user must account for format sensitivity increasing the expected count rate according to the values given in Table 6.4 (see "Format-dependent Effects" on page 75).
In support of COSTAR, FOCSIM has been upgraded to allow for automatic selection of the COSTAR imaging modes. The latest DQE tables are available for use with FOCSIM for both of the relays. These can be selected in the FOCSIM setup and can be found in the FOCSIM auxiliary directory. In addition to the new DQE tables, theoretical PSFs have been produced to simulate COSTAR corrected FOC PSFs and observed PSFs taken with the COSTAR-corrected FOC have been added to the FOCSIM libraries. Using the updated DQE tables and PSFs allow FOCSIM to simulate COSTAR corrected observations with accuracies dominated by the errors inherent in the PSFs, primarily from small changes in focus or position in the COSTAR-corrected field of view. Initial experience in Cycle 4 has indicated that errors of about 10% in the simulated count rates for the 512 x 512 format should be expected.
The output of FOCSIM includes all relevant information on the input parameters selected, the appropriate instrumental parameters and subsidiary data such as the individual components of background, the monochromatic count rate shown in Figure 6.14, restrictions such as NMAX, data on the magnitude of the red and blue leaks, and, of course, the resultant exposure times. The user can also request that FOCSIM output the transmission curves for the filters and the source spectra as IRAF SDAS tables, which can subsequently be plotted using IRAF procedures.
FOCSIM will be made available at the STScI to interested users of the FOC who have local accounts. Unfortunately, FOCSIM is not available for general distribution along with STSDAS for a couple of reasons: first, it uses additional libraries which are prohibitively large, and secondly, it does not conform to IRAF's standards for software programming. A beginner's manual is available upon request from STScI, either as a PostScript file or a printed version. It describes the basic steps necessary for running FOCSIM by walking through a sample session. The manual also provides a list of the catalogs of spectra that are available for use with FOCSIM and samples of the output which FOCSIM produces. Additional on-line help has recently been added which can be accessed through the standard IRAF help facilities.
Generated with CERN WebMaker