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Observation Preparation & Execution

Most VLBA observations are scheduled dynamically, based on array and weather conditions predicted 1-2 days in advance. Users allocated VLBA observing time, either on fixed dates or on a dynamically-scheduled basis, will be sent instructions for preparing observing schedules.

Most VLBA observations are scheduled using the VLBA SCHED program (Walker 2011). SCHED includes a variety of extremely useful facilities cross-linking and error-checking the many options available for VLBA observing, and substantially simplifies the overall scheduling process. A comprehensive SCHED User Manual includes instructions for obtaining and installing the software. Help with preparing VLBA observations is available through the NRAO Helpdesk.

One of the many useful features of SCHED is a table of angular distance between each scheduled source and the Sun, with an accompanying table of safe angular distance as a function of observing frequency. Some users may have external information on how close to the Sun their source(s) may be, and would like to consult the table of frequency dependencies without having to generate a complete SCHED input file. That table is reproduced below.

Table 17.1: Minimum angular distance between source and Sun

Observing Frequency (GHz)

Minimum Solar Distance (deg)

0.33 117
0.61 81
1.6 45
2.3 36
5.0 23
8.4 17
15 12
22 9
43 6


Each VLBA program is run remotely from the SOC by VLBA operations. No observing assistance by a VLBA user is expected, although VLBA operations should be able to reach the observer by telephone during the program, at a number that should be specified in the schedule file. As the program progresses, the array operator monitors the status of the antennas and the station data path. Logging, calibration, and flagging data are automatically recorded by the monitor and control system. If necessary, the array operator can request local assistance from a site technician at each VLBA station. Recorded media are automatically shipped from each VLBA station to the correlator specified by the observer.