CFH12k Queued Observing Programme: Preliminary Description.


5. Queue execution.

 Following is a rough outline of the decision tree which is applied in the process of queue execution. This is expressed as a flow diagram in Section 6.

5.1. Viability.

The following criteria must be met by a programme group for it to be considered viable for observation:

Observing feasibility criteria:

5.2. On completion of a programme group.

 After a programme group is completed, or at the beginning of observations for the night, the queue database engine performs the following tasks:

    1. Add up total I-time & overhead still required by started programmes.
    2. Compile complete list of currently viable programmes, ordered according to TAC ranking. These operations may be performed entirely automatically. Therefore, there is no reason not to repeat them after every exposure, thus providing the observer with a constant update on the state of the queue according to current conditions. The observer may also force a recalculation if, for example, the seeing degrades, tranparency improves, etc. or if he wishes to anticipate the next exposure, he may refresh the queue during the current exposure on the assumption that this exposure completes successfully.

      One of the following three condition/response combinations will then apply:

  1. If the list of viable programmes contains started programmes, the unstarted programmes are discarded and the next observations are taken from the started, viable programme with the highest TAC ranking. If there is more than one viable group in this programme, the particular group to be observed is chosen at the observer's discretion, taking into account the current telescope pointing, instrument configuration, sky conditions, etc. It is therefore in the investigators' interest to specify some guidelines under these circumstances (some indication of the relative priority of each group).
  2. If the two highest ranking, viable, started programmes have identical TAC ranking, the programme to be observed is that with the least remaining I-time to consume.
  3. If there is no started, viable programme, the next programme to be observed is the unstarted, viable programme with the highest TAC ranking. If the two highest ranking, unstarted programmes have the same TAC ranking, the choice of observations will be at the observer's discretion.
  4. If there are no viable programmes, the observer may expand the envelope which defines viability and refresh the queue. For example, she may expand the range of allowed airmasses for observations and repeat the above algorithm. Alternatively, she may wish to adjust the measured seeing value to be slightly more optimistic.
  5. Such artificial adjustments will apply for one exposure only, after which the queue reverts to its normal state. The investigator whose data are collected under these circumstances will be informed immediately and consulted on the usefulness of the data. Thus, if a started programme becomes viable while another programme of lower rank is running, the current observation group for the executing programme is completed and then the higher ranked programme takes over.

    The observer will be provided with list of observation groups to execute as each observation group is completed ordered according to TAC ranking and following the above rules. Normally, the observation group at the top of this list will be executed next, but the observer is presumed to be best able to assess the current observing conditions and observations made so far and may therefore override this choice.

    For a graphical representation of these rules, see Section 6.



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