Service Mode Rules and Recommendations for Observation Blocks

Preparing Observation Blocks

Both Visitor and Service Mode programmes are carried out at all ESO telescopes by executing Observation Blocks (OBs) provided by the users. OBs are constructed and submitted to ESO using the P2PP version 3 (P2PP3) Tool for all Paranal instruments.

Please refer to the P2PP3 User Manual and to the User Manuals of the different instruments for more specific information on the structure and contents of OBs, and how to build OBs for different instruments. A number of tutorials describing step-by-step the construction of OBs for different instruments is available.

Service Mode OBs: rules and advices

It is important to keep in mind the Service Mode policies and the following rules and guidelines when designing a Service Mode programme or when preparing a Phase 2 package:

  • Some observing strategies cannot be supported in Service Mode; in particular, real-time decisions about the sequencing of OBs, complex OB sequencing, or decisions based on the outcome of previously executed OBs (like adjustment of integration times or execution of some OBs instead of others).
  • OBs are only executed once. If you want to repeat an identical observation multiple times, you must submit multiple OBs. This requirement applies to standard stars as well.
  • OBs are normally executed non-contiguously. Since efficient Service Mode operations require continuous flexibility to best match the OB constraints with actual observing conditions, OBs for a given programme are normally scheduled non-contiguously. Therefore, users should not expect their OBs to be executed on a specific sequence or in a linked way, unless a sound scientific justification (indicated in the README file and approved with a Phase 2 Waiver in case of a contiguous execution lasting longer than 1 hr) exists. Approved OB sequences should then be prepared as concatenations. Exceptions to this rule are cases in which one OB observing a calibration source needs to be executed contiguously to a science OB. In such a case place both OBs into a concatenation scheduling container to enforce their contiguous execution.
  • Multi-mode, multi-configuration OBs are normally not permitted in Service Mode. Although multiple configurations within one OB may sometimes reduce overheads, scheduling and calibrating such OBs is extremely inefficient and can increase the calibration load to an unsustainable level. Examples of such multi-configuration OBs are those combining imaging and spectroscopy in a single OB, spectroscopy with multiple grisms or central wavelength settings, or imaging with a large number of filters (although most imagers allow multiple broadband filters in one OB). Multi-configuration OBs are accepted only if duly justified and authorized by means of a Phase 2 Waiver Request.
  • OB execution times must be below 1 hour. Long OBs are more difficult to schedule and execute within the specified constraints because of the unpredictable evolution of the observing conditions. For this reason,OBs taking more than one hour to execute time are accepted by ESO only in exceptional cases and provided that a Phase 2 Waiver Request is submitted and approved. In such cases, ESO will consider the OB successfully executed if the constraints were fulfilled during the first hour of execution, even if conditions degrade after that time.
  • Concatenation scheduling container execution time must be below 1 hour and exceptionally for CRIRES instrument science+telluric standard concatenation must be below 1.5h. Only in exceptional cases, and provided that a Phase 2 Waiver Request is submitted and approved, longer concatenations may be submitted. In such cases, ESO will consider the concatenated OBs successfully executed if the constraints were fulfilled during the first hour of execution, even if conditions degrade after that time.
  • User-provided calibration OBs that need to be executed contiguously with science OBs need to be specified via concatenation scheduling container.
  • Time constraints must be indicated in the OBs. If you intend to observe time-critical events or monitor a target at specific time windows, you need to indicate this under the Time Intervals tab of the OBs. For monitoring observations it is often more appropriate to put OBs in a time-link container. Specifying time windows as broad as possible will reduce the possibilities that your OBs are not executed because of higher priority programmes or because the external conditions did not allow the observations during the interval that you specified. Please read carefully the time-critial OB execution policy.
  • Specify the weakest possible Constraint Set values. OBs that can be executed under a broad range of conditions are easier to schedule, especially if they belong to priority groups B or C. In particular, if photometry is needed of a field, it is normally sufficient to obtain a short integration under photometric conditions (transparency = PHO) and carry out the rest of the integration with OBs having a transparency = CLR constraint.

Additional Service Mode Requirements for KMOS

Selected DIT Values

In order to prevent daytime calibrations (dark frames) to run for a large fraction of the morning, it is recommended to limit the use of different DIT values to a minimum set (2.5, 3, 4, 5, 10, 15, 20, 30, 60, 100, 300,  450, 600, 900, and 1200 seconds). It is mandatory to select one of these values for DIT longer than or equal 300 seconds. Different DIT values would need a waiver. A DIT of 1200s is only allowed for the IZ band.

Note that the background limited performance between the OH lines is reached in 300s.

Saturation and persistence limits

It is important to avoid saturation of the detectors because the persistence artefacts can last up to several hours and thus affect subesequent observations.

Therefore, targets should not be brighter than 6th magnitude in J,H,K bands.

There are also persistence effects for illuminations of >40.000 ADUs/DIT/pixel. Please make sure, with the help of the ETC, that such fluxes are avoided for your brightest targets, even for better conditions than foreseen (e.g. using seeing 0.4" in the ETC).

Absolute offsets

Please note that, unlike as for all other VLT instruments, the offsets (e.g. dither, etc.) for KMOS are defined in an absolute sense, referring to the initial pointing position. I.e. the offsets are not cumulative, relative to the previous position.

Rotator optimization and priority 1 targets

Rotator optimization is applied if one or more arms are locked for a certain period due to technical problems. In this case, the instrument is rotated in such a way that the maximum number of priority 1 and 2 targets are covered by the available arms.To make this work it is important that the science targets have a range of priorities from 1 to 3.

Some KMOS acquisition templates allow to suppress the rotator optimization. This might be useful if you want to enforce that your main target is on a certain IFU or if you need to make sure that 3 IFUs allocated on sky, i.e. one per detector, keep their positions (but look at the KMOS news whether these arms are indeed available). Note, however, that in this case you accept that more than 10% of your priority 1 targets can get lost.


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