Observer-Imposed Constraints: Definitions

Observer-Imposed Constraints

The constraints available to observers are:

Chain (ordered, non-interruptible group)

The AORs will be executed in the order specified with NO interruptions in the chain. If you chain together AORs, you must ensure that the chain does not exceed the maximum allowable duration for a single AOR (3 hours for MIPS, 6 hours for IRS and IRAC). Spot will warn you if your chain is too long. It will show you the total time in the chain in the constraints window.

Sequence (ordered, interruptible group)

A sequence constraint is similar to, but less stringent than, a chain constraint. The AORs will be executed in the order specified and a duration in which they should be completed is specified. The sequence constraint should only be used when the science requires sequential ordering of the AORs. For AORs in which the order of observation is not important, a "group within" constraint (see below) should be used instead of a sequence constraint.

Group-within

A group-within constraint specifies that a group of AORs will be executed within a specific length of time but with no particular starting date/time constraint. Once the first AOR has been executed, the rest of the AORs in the group will begin within the specified time interval. They may be executed in any order within the time interval. This is similar to a sequence constraint, but the observations may be executed in any order.

Timing

Timing constraints consist of defining a window or series of windows for the start time of an AOR. If the open and close times of the window are specified to be identical for a moving target, then the AOR will be scheduled as an absolute time observation at that time, and will be executed at that time or no more than 3 seconds later. Spitzer's scheduling architecture generally operates on relative time, so for inertial targets, the (inertial target) AORs will simply run in order. Timing constraints for inertial target AORs should be macroscopic (days, weeks, months), not microscopic (seconds, minutes, hours). Spot will warn you if you set a timing constraint such that the target is not visible for some portion of time within the timing window, but will still allow you to set the constraint.

Follow-on

A follow-on constraint executes the 'follow-on' AOR within a specified time range after a particular initial AOR has been executed. (In other words, from the end of the first AOR to the beginning of the second AOR.) An instance in which this constraint might be used is when the observer wishes to perform an IRS "peak-up only" observation to confirm target placement before starting (perhaps much later) a second observation to actually obtain spectra of the target. This constraint could also be used for periodic observations of a target where the interval between observations is relatively short (hours to a small number of days).

Shadow

The shadow constraint is a special case of the follow-on constraint, and is used to obtain background measurements for moving targets. The primary AOR is executed as specified. The shadow AOR will be executed to repeat the track of the primary observations. The selected AOR parameters must be identical in the two AORs. The shadow may be executed before or after the primary AOR. Note that the shadow does not re-observe the target at a later date, but rather the background of the primary observation.

Go back to main Constraints page