Special Overhead Burdens

Special Overhead Burdens

Special overhead burdens are applied to:

1. observations of high-and medium-impact Targets of Opportunity (ToO),

2. rapid non-sequential instrument observations of a target, and

3. solar system targets with a late ephemeris change.

These special overheads are added to the normal overheads applied to each Astronomical Observation Request (AOR) computed by Spot, the software required for Spitzer observation planning and proposal submission. They represent current estimates of the time required to prepare for the observation and to return the Telescope to its nominal configuration and schedule. As described in §15.1 of the Spitzer Space Telescope Observing Rules (Appendix A), the special overheads are intended to reflect the observing time lost in other programs as a result of executing the relevant observation(s).

For observations in categories (1) and (2) above, it is deemed that access to the source in a timely manner is more important than the calibration accuracy. The advantages of stable operations within a normal instrument campaign of 7-21 days are compromised in these quick-turnaround scenarios, and the Principal Investigator needs to ensure that the data collection is sufficiently robust to meet reliability and calibration accuracy requirements.

In evaluating General Observer proposals, peer reviewers will assess the value of observations with special overhead burdens against other proposed observations. Proposals must include these overheads in the total requested observation time. The special telescope overheads are listed below.

High-Impact Target of Opportunity, Single Instrument: 6.5 hours

This overhead will be applied to the first AOR in a group, chain or sequence of AORs to be executed consecutively during a single observing session on a single ToO with one science instrument. For observations that are constrained with a follow-on constraint, the overhead must be applied to every AOR individually. The group, chain or sequence constraints mean observations can be scheduled contiguously and therefore have less impact on the schedule than those constrained with a follow-on constraint.

High-Impact Target of Opportunity, Multiple Instruments: 8.8 hours

This overhead will be applied to the first AOR in a group of AORs to be executed consecutively during a single observing session on a single ToO. Either two or three instruments may be used if the observation is constrained in a manner that allows the instruments to be used in any order. For observations that are constrained with a follow-on constraint, the overhead must be applied to every AOR individually.

Medium-Impact Target of Opportunity, Single Instrument: 2.6 hours

This overhead will be applied to the first AOR in a group, chain or sequence of AORs to be executed consecutively during a single observing session on a single ToO with one science instrument. For observations that are constrained with a follow-on constraint, the overhead must be applied to every AOR individually.

Medium-Impact Target of Opportunity, Multiple Instruments: 5.2 hours

This overhead will be applied to the first AOR in a group of AORs to be executed consecutively during a single observing session on a single ToO. Either two or three instruments may be used if the observation is constrained in a manner that allows the instruments to be used in any order. For observations that are constrained with a follow-on constraint, the overhead must be applied to every AOR individually.

Non-Standard Sequential Observations: 2.6 hours per instrument change

The normal cycle of scheduled instrument campaigns (of 7-21 days duration) will be IRAC-MIPS-IRS-IRAC, etc. Requests for observations, to be executed in rapid succession, that violate this sequence will be assessed additional overheads per instrument change. For example, a request for IRAC observations, followed shortly thereafter by IRS observations, will be assessed an additional 2.6 hours of overheads. A request for near-contemporaneous observations of a target with all three instruments will be assessed 5.2 hours of special overheads.

Late Ephemeris Update: 0.5 hour