Building Sequence Database Files for the Hopkins Ultraviolet Telescope

Count rates are most readily determined by running the program "HUTSIM2" which we have made into an IRAF task. It has a detailed on-line `help' file, and is described in more detail in the HUT Handbook. This flexible program can receive or calculate input spectra in a variety of formats, incorporate the effects of reddening, and basically do just about anything one needs to do to estimate an expected count rate. For an assumed aperture size, count rates are calculated (both with and without airglow emissions) and output for each run of the program, along with IRAF-format and/or ascii output files of the input and output spectra. (You may wish to save the final HUTSIM parameters and ascii counts output files for use with the target book. See section 4.) By consensus, we enter the count rate without airglow into the SDF parameter `Initial_expected_rate.' Airglow counts get added to the sequence load automatically by the BUILDSEQ program.

As described in the HUT Handbook, we impose both a total count rate limit across the array (5000 cts/s) and a peak count rate limit for emission lines (40 cts/s/pixel) for detector safety reasons. In addition, objects with expected count rates below 500 cts/s can be observed in "high time rate" mode (where each photon is "time tagged") as opposed to "histogram" mode (data saved every two seconds). HUTSIM outputs should be checked for consistency with these limits. If the anticipated count rate is too high, one can attenuate the count rate by selecting another spectrograph aperture (for extended sources) or by choosing alternate aperture door states, as described in the HUT Handbook. Attenuations of a factor of 2, \(ap100, and \(ap1250 are available. The appropriate coded entries for the `Primary_slit' and `Door_config_#' are entered in the SDF.

In addition, for Astro-2 the capability for "partial door states" has been added. This procedure opens the main aperture doors by an amount specifiable by the user to optimize the expected count rate. Users should be aware that calibration of partial door states may be somewhat less accurate than the discrete door states, although current plans call for calibration of one or two specific partial door states, depending on demand. If you want to use a partial door state, set the `Door_config_#' parameter to 2, set the optional parameter `Partial_door_opening' to be the desired fraction of full aperture, and use one of the `PT_DOOR#' target procedures provided in Appendix C. Partial door states should only be used in those cases where the simulated spectrum is high enough fidelity to provide an accurate expected count rate.