Concatenated observations are a chain of observations from the same proposal which have to be performed contiguously in time. All targets of the concatenated observations must lie in an area of 3 degrees diameter.
For scheduling, concatenated observations are treated as a single unit, i.e. either all observations in the chain are scheduled or none. The underlying rationale for this treatment is that the proposer uses concatenation to indicate that scheduling of only a part of these observations is not sufficient to meet the scientific objectives described in the proposal justification.
Note that concatenating observations simply because the pointings are close together in the sky is not a valid argument, since the mission planning system optimises the schedule very efficiently.
In principle up to 99 observations, i.e. the maximum allowed per proposal, can be concatenated. However, the more AOTs are contained in the chain, the longer the duration of the entire observation; once this duration exceeds several hours, it becomes highly unlikely that the observation can be scheduled.
The nominal overhead for slews between concatenated observations is 20s.