How the APF Scheduler Works

The Basic Selection Loop

The APF Scheduler currently follows the steps below. Items in bold are part of the Target Specification.

  1. Select all non-calibration stars (removes B stars and others.)
  2. Mark the previous target, if any, as observed or attempted
  3. Remove all targets that have been observed within their desired cadence window, APFcad, - note that stars can reappear in a night if need be by have that value be small enough, also remove targets that were attempted but failed
  4. Remove targets that are too close to the moon, which is a time dependent value from 15 to 25 degrees depending linearly on the phase
  5. Remove observations that take longer than 3 hours or will be finished after sunrise. When within 20 minutes of sunrise, all 20 minute observations are kept (An observation has a duration of texp multiplied by APFnshots)
  6. Remove all stars that are below the horizon or will be at the end of the exposure, or will pass above an elevation of 85 degrees during the exposure.
  7. Remove faint stars (V >9) if poor seeing or poor transparency
  8. Rank the remaining targets by priority. The final priority is based on the grade assigned by the TAC, the internal priority assigned by the observer APFpri, and finally whether or not the program has exceeded its allocation for the night, see below
  9. All remaining targets at the highest priority are compared. The target closest to transiting the meridian is then selected.

Components of the Scheduler that Control Target Priority

The scheduler has three pieces that determine the ranks or priorities of a target

  • Program Grade
  • Internal Priority
  • Allocated Fraction of the Night to a Program

Grade and fraction of the night are allocated by the APF TAC. The grade is the most important and the internal priority can never be high enough to move a target from one grade to another. Within a given grade, internal priorities are used to determine which star has the highest priority.

Programs are allocated fractions of a night. The program fraction is proportional to the total allocation of hours for 1000 hour semester. The minimum fraction is set to 10%, however.

The fraction used by a program is only computed after the most recent observation.Therefore, a program is turned off when the fraction is exceeded. A small program that needs, for example, a one hour observations will also be able to conduct those observations even if the nightly fraction would fall below that. Once the observation is made, however, the program cannot take any more data for that night.


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