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 SINFONI

These observing modes are not offered:

  • observations with the sky spider
  • observations with spectral dithering

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 (0.83, 1, 2, 5, 10, 15, 20, 30,60, 100, 150, 300, 600, 900 seconds). It is mandatory to select one of these values for DIT longer than 150 seconds. The choice of the DIT should also take into account the possible detector persistence effects (please check Table 2 )

Magnitude limits for natural guide stars and targets

R-band NGS LGS     
 max 2a 12
  min 14b 17c

Note (a): Stars brighter than R-band ~ 2mag cannot be used as AO reference because they would exceed the 10^6 ADU saturation limit for the APDs.

Note (B): Observations using an AO reference star fainter than R-band ~ 14mag (down to R~17) are possible  only under tight weather condition (Clear/seeing < 0.6").

Note (c): Observations using a Tip-Tilt star as faint as R~18 are possible under very tight weather constraints but the correction will be very poor.

The SPIFFI detector has a persistence effect, even after being illuminated below the saturation level (typically ~ 10 000 ADUs), that can last for many hours if the observed sources are too bright. In Service Mode, this problem can affect subsequent observations of other programs. To exclude any risk of artifacts produced by wavelength-dependent detector persistence, given the magnitude of your target and the requested seeing conditions, the DIT must be selected checking that the predicted fluxes do not exceed the values (ADUs/DIT/pixel)  listed in the table below.

         J             H            H+K          K        
  6000 7000 7000 8000

Observations of point-source targets brighter than J/H/K/-band = 5mag or (H+K)-band = 6 mag are therefore not allowed in Service Mode, except if acquisition is performed via SINFONI_IFS_acq_NGSfast, and if the 25mas scale is used for the science template. Observation of such bright targets requires the submission of a Phase 2 Waiver Request.

Angular Size of the AO Reference Object

The WFS FOV is 3.6" on the sky. Therefore, the angular extent of the AO reference source should be much smaller than this. If you use an extended object as AO reference source (i.e. galaxy nucleus) then make sure that at visible wavelength it has a very contrasty core (i.e. nearly point-like).

Telescope guide star

For any NGS fainter than 11 magnitudes it is mandatory that the telescope guide star coordinates are given by the Users (in the acquisition template: Telescope Guide Star Selection == SETUPFILE). The reason for this is that inaccuracies (~1") in the telescope and/or NGS coordinates cause the target to fall off the small field of view of SINFONI.

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