Some portion of projects on the VLBA are now being scheduled dynamically. That means that they are put into a special queue, along with information about their minimum requirements, and then are run at an appropriate time given the weather and condition of the equipment. The hope is to increase the overall quality of VLBA output by avoiding observations at times when it is clear that the results will be poor. For example, there is not much point in observing at 43 GHz when there is bad weather at many sites. But a 1.6 GHz observation at the same time might be fine. Dynamic scheduling also allows more flexible response to targets of opportunity. Galactic sources, in particular, tend to have short periods of enhanced activity so it is best to be able to observe when they are high. Of course, it is possible that some projects in the dynamic scheduling queue will never be scheduled.
The PI for a dynamically scheduled project will be given a window in LST at the VLBA_PT (Pie Town) that will be scheduled, if the observation is done. In addition, there will be a wider window that might be scheduled. The PI should prepare a schedule using the LST parameter with Pie Town as an argument (LST=VLBA_PT). It should cover the entire time over which observations might be scheduled. All critical scans, especially calibrators, should be scheduled in the guaranteed time as the extensions to that might not be observed.
When a program is selected for a dynamically scheduled time slot, VLBA operations personel will modify the date (calendar or lst day number) to match the scheduled day. This last minute modification is necessary because the stations do not have an LST concept and the machine readable files delivered by SCHED must be in UT. The files will then be loaded to the sites with instructions about the time window to use, which may well be a subset of what is actually in the schedules. Because of this last minute modification of the date, it is best to minimize the use of dates in the SCHED input. Use durations instead.