Service Mode Rules and Recommendations for Observation Blocks

Preparing Observation Blocks

Observations at all ESO telescopes are carried out by executing Observation Blocks (OBs) provided by the users. OBs for Service Mode runs at UT2 (i.e. using FLAMES, UVES and/or XSHOOTER), VISTA (i.e. VIRCAM) and VST (i.e. OMEGACAM) must be made with p2. OBs for all other Service Mode runs with Paranal Instruments must use P2PP version 3 (P2PP3). For (designated) Visitor Mode observation preparation, please follow dedicated Visitor Mode Guidelines.

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 may be 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 multiple 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.  Usage of absolute time intervals must be scientifically justified in the README file. 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. 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 VIRCAM

The easiest and recommended way to prepare the OBs for VIRCAM on VISTA 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 ancillary 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. It is recommended to use SADT even in cases where only a single pawprint is observed per OB - for that tile1 template should be used.

With the web-tool p2 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.

Important notes and OB rules:

  • The Tile Pattern has to be chosen already in SADT. Do not change the Tile Pattern in p2 after importing the survey definition (XML) file to your OBs!
  • The Maximum Jitter Amplitude has to be set in the SADT configuration file that is located in the SADT installation subdirectory cfg/vista/sadt.cfg. It must have consistent size with the Jitter Pattern selected in the OBs in p2.
  • Do not change the target coordinates in p2 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.
  • ToO observations: The most appropriate set of templates to use for TOO observations are the VIRCAM_img_acq_quick acquisition template in combination with the VIRCAM_img_obs_paw science template. The following parameters must be set in the acquisition template for ToO programmes in order place the image of the target (OB pointing coordinates) in Chip 11:
Parameter Value
TEL.TARG.X "39.0"
TEL.TARG.Y "-29.3"

            Selection of different parameters in the VIRCAM_img_acq_quick template requires an approved waiver request.

  • OBs requesting seeing better than 1.0", which have (DIT+2)*NDIT shorter than 45 seconds, must set AO priority "HIGH" in the OB, or in the first OB of each concatenation. In exceptional cases OBs with AO priority "NORMAL" requiring seeing < 1.0" and having (DIT+2)*NDIT<45 sec may be accepted by ESO provided that a Phase 2 Waiver Request is submitted and approved.
  • OBs containing more than one filter must have one filter per each observing template, unless using PFJME nesting. In exceptional cases multiple filters per template may be granted also for other nesting options provided that a Phase 2 Waiver Request is submitted and approved.
  • Please run the verify script before submission and carefully read the WARNING messages if they appear

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