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 Phase II Proposal Preparation (P2PP) tool. Please refer to the P2PP 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 II 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 (to be approved with a Phase II Waiver and indicated in the README file) exists. Exceptions to this rule are cases in which one OB observing a calibrations source needs to be executed contiguously to a science OB.
• 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). Multiconfiguration OBs are accepted only if duly justified and authorized by means of a Phase II 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 II 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.
• User-provided calibration OBs that need to be executed contiguously with science OBs need to be indicated in the User comments entry of the relevant science OBs.
• 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. This information needs to be provided also in the corresponding section of the README file. 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.
• 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.

Exceptions to the General Service Mode Rules for VIRCAM

For service mode observations with VIRCAM the above given general rules apply except that now some specific observing strategies are supported:

• Contiguous execution of OBs: The new Phase 2 Preparation (P2PP) for Surveys tool allows the definition of "Concatenation" containers, in which a series of OBs is executed consecutively. The total execution time of such a container must not exceed 1.5 hours. In exceptional cases "Concatenation" containers taking more than 1.5 hours can be accepted by ESO provided that a Phase II Waiver Request is submitted and approved.
• Time-linking of OBs: Apart from the absolute time constraints that can be defined in the Time Intervals tab of the OBs, the new Phase 2 Preparation (P2PP) for Surveys tool allows the definition of "Time Link" containers, in which relative time links for a series of OBs can be specified.
• User-provided calibration OBs that need to be executed contiguously with science OBs must be concatenated with the science OBs.
• Time constraints must be indicated in the OBs. All time constraints have to be defined via the Time Intervals tab of the OBs and time link containers. The README file does not need to contain information for time windows for any OB of public survey runs.

For further information about different observing containers that can be used to specify observing strategy for surveys please see P2PP for Surveys User Manual.

Additional Service Mode Requirements for VIRCAM

The easiest and recommended way to prepare the OBs for Public Surveys with VISTA and VIRCAM is to first run the Survey Area Definition Tool (SADT) to generate the list of central coordinates of pointings for each tile, together with the ancilliary information about the available guide stars and active optics (aO) stars. In particular, for surveys that are using tile patterns with three or six offsets, the use of SADT is mandatory.

In the Phase 2 Preparation (P2PP) for Surveys. the user defines the template OB, or alternatively, if necessary, the template container (group, time-link or concatenation of OBs) with its sub-structure, and selects all the parameters relevant for the survey (templates for acquisition and observation, filter(s), exposure times, jittering strategy, observing constraints, and OB execution time windows and priorities), except the target coordinates. The output of SADT, the survey definition file in XML format, is then imported to the template OB or container. This action duplicates the OBs (and containers) and supplies the information about pointing coordinates, guide stars and aO stars, and so automatically generates the OBs ready for execution.

Tutorials that describe how to define a survey area and how to prepare the VIRCAM OBs are available here.

Some importants notes:

• The Tile Pattern has to be chosen already in SADT. DO NOT change the Tile Pattern in P2PP after importing the survey definition (XML) file to your OBs!
• The Maximum Jitter Amplitude has to be set in the SADT configure panel, and has to have consistent size with the Jitter Pattern selected in the OBs in P2PP.
• DO NOT change the target coordinates in P2PP after importing the survey definition (XML) file to your OBs!
• Do not manipulate any coordinate in the survey definition (XML) file by hand!
• The use of microsteps is discouraged. Tests during commissioning have shown that microstepping leads to distorted PSF shapes and problems for photometry.