The Programme Priority Groups

All programmes allocated observing time in Service Mode are assigned to one of the following priority groups:

  • Group A: High Priority: These programmes are considered to have the highest scientific value and are executed first as observing conditions allow. ESO makes every possible effort to complete programmes in this Group. This includes the possibility of carrying over programmes in this category to the next semester, in case that their degree of completion at the end of the allocated semester is too low for the fulfillment of the scientific goals. Large Programmes are automatically considered as high priority programmes. Within group A they are ranked higher than normal programmes. Target-of-Opportunity (ToO) programmes cannot be considered for carryover status. All PIs of programmes in this group are informed about one month prior to the next Call for Proposal deadline about the carryover eligibility of their programme.
  • Group B: Medium Priority: Programmes in this group have lower scientific priority than Group A and are executed only when no Group A programme can be executed. ESO tries to complete all programmes in this Group, but incomplete programmes are terminated at the end of the allocated semester. The likelihood that any given Group B programme is executed decreases as more stringent observing constraints are requested.
  • Group C: Low Priority: These programmes have lower scientific priority than those in Groups A and B but have relaxed constraints (see below), which allows them to be scheduled when the external conditions are not suitable for the execution of any programmes in Groups A and B. The programmes in Group C would not have been scheduled if Visitor Mode had been the only observing mode offered by the Observatory. However, the flexibility of Service Mode scheduling allows in this way a scientifically valuable use of the telescope time even under conditions that would be unsuitable for the execution of higher-ranked programmes.

The webletter (or email in the case of DDTs), prepared by the Observing Programmes Office (OPO), states which Group your programme was assigned to.

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