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 content 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 in 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 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 containers.
  • 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. Please note that absolute (UT) time constraints refer to the interval in which the OB can be started, whereas for Local Sidereal Time (LST) time intervals, the time interval refers to the entire duration of the OB. 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 observing 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 VLTI

Target coordinates

Special care should be taken when entering the target coordinates in P2PP. We have made the best experience with 2Mass coordinates. Also, to ease fringe finding during the observations, proper motions of the target (if available) must be entered in P2PP.

Visibility Calculator

To prepare and plan your VLTI observations, we recommend to use the Visibility Calculator VisCalc. The assessment of the feasibility of an observation requires an estimate of the expected visibility for the chosen VLTI configuration, as well as of the observability of the target in terms of altitude, the limited delay line strokes, and shadowing effects.

Aperture Synthesis

The scientific goal of an interferometric observation campaign can often only be reached if visibility measurements at different projected baseline lengths and/or baseline angles are combined. The visibility calculator VisCalc provides calculations of simulated visibilities as a function of baseline configuration and hour angle, so that the best suited combination of baseline configuration and hour angle (or Local Sidereal Time, LST) can be identified.

Each OB must specify a certain baseline configuration (one AMBER triplet out of the Phase1-assigned quadruplet or one PIONIER quadruplet) and the desired range of LST. Please note that restricting the LST is more constraining than choosing different baseline configurations, and that in the past we have noticed that the execution of OBs with relatively large LST intervals is more efficient. Whenever possible, it is thus recommended to fill the uv-plane by making use of different baseline configurations within the assigned AT quadruplet rather than by using different LST intervals.

In case that, from a scientific point of view, there is no restriction for the LST range to be used, the LST range in the OB must reflect the range when the target is higher than 30 degree (40 degree if FINITO is used) above the horizon, and exclude the range when the observation is not feasible due to delay line restrictions or shadowing effects.

Sequences of science targets and calibrators

Interferometric observations require the frequent measurement of interferometric calibrators. VLTI OBs must be submitted as sequences of science target OBs (SCI) and calibrator OBs (CAL) and must make use of concatenation containers in P2PP. This means that every VLTI OB must be submitted as a part of a concatenation. Each concatenation must normally include a CAL-SCI-CAL sequence. SCI-CAL sequences are also accepted for AMBER only if the scientific goal of the observation is mostly a wavelength-differential measurement and if the absolute visibility calibration is not the main goal. CAL-SCI-CAL-SCI-CAL sequences are generally available for PIONIER, and upon a waiver request for AMBER. Please also note the VLTI-specific naming rules for science target and calibrator OBs.

Every concatenation is executed once. If an observation of a scientific target shall be repeated at different LST intervals or with different baselines, there must be as many concatenations submitted as desired observations.

Additional Service Mode Requirements for AMBER

An overview on the offered baseline triplets since P96 and their pointing restrictions can be found at

AMBER observations using the LR mode with a seeing constraint of 1.2 arcsec and THN conditions can now also use a CAL-SCI-CAL-SCI-CAL sequence upon approved waiver. More details can be found on the CfP page. Regular rules regarding successful execution of containers with long execution times apply, i.e. the grading will be based on the first CAL-SCI-CAL sequence only.


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