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 all Service Mode programmes using Paranal instruments are constructed and submitted to ESO using the P2PP version 3 (P2PP3) Tool. 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 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 VIMOS

General VIMOS Requirements

Here are listed specific requirements that apply to all VIMOS OBs.

One VIMOS mode per OB

VIMOS is offered in imaging (IMG), multi-object spectroscopy (MOS), and integral field spectroscopy (IFU) modes. As a general rule, observing modes of the instrument must not be mixed within a single OB. This implies that each OB should contain the acquisition and observation description templates corresponding to the selected instrument mode.

It is possible to concatenate imaging and MOS observations, such that the two OBs are executed back-to-back. The concatenation of IMG and IFU, as well as MOS and IFU OBs is not allowed, because the deployment of the IFU does not make this change of observing mode efficient to schedule in Service Mode.

VIMOS standard configuration

The standard configuration of permanently installed optical components (filters, grisms) is given in the VIMOS User's Manual. No other grisms and filters are allowed either in service or visitor mode.

The configuration is the same for the 4 channels. All components of the VIMOS standard configuration remain at their nominal location inside the instrument at any time.

VIMOS standard CCD setup

Only the standard CCD setups described in the VIMOS User's Manual are offered both in service and visitor mode. Windowing of the CCDs is not supported.

VIMOS Field-of-View and Orientation

For pre-imaging and the follow-up spectroscopy the orientation of the VIMOS Field-of-View on the sky must be with rotator angle at 90 degrees for targets with a declination below -45 deg and above -5 deg, such that the slits are oriented along the N-S direction. For targets between -45<DEC<-5 deg the rotator angle can be either 90 degrees or 0 degrees (slits oriented along the E-W direction). Deviations from these default values must be specifically approved by ESO before you submit your Phase 2 information. Please use the Phase 2 Waiver Request procedure for this purpose.

Quality control grading of VIMOS

As stated in the Call for Proposals, any set of MOS data obtained with VIMOS in Service Mode where at least 3 of the 4 arms functioned will be considered an observation completed within constraints.

Specific Requirements for Pre-Imaging

VIMOS Pre-Imaging is recommended prior to MOS follow-up. All MOS programs with pre-imaging must have a specific Run ID devoted to pre-imaging (i.e., a typical MOS programme consists of a run (A) devoted to pre-imaging, and a run (B) for the ensuing MOS). The following instructions for preparation of pre-imaging OBs should be strictly followed:

  • Run ID: It is mandatory to use the Run ID corresponding to the pre-imaging run. Please check your Phase 1 proposal if you are unsure as to which run is the one for pre-imaging.
  • Observation Category PRE-IMAGE: It is mandatory to set the Observation Category to PRE-IMAGE in the observation template (VIMOS_img_obs_Offset). Failure to do so will result in delays to process and deliver the pre-imaging data, and may result in MOS observations not being carried out.
  • Pre-imaging Filter R: Because the mask to CCD solution is computed using R filter, pre-imaging taken with R filter is mandatory in order to minimize the slit losses. Should any other filters be required, users must apply for a Phase 2 Waiver before these pre-imaging OBs can be accepted.
  • Rotator on sky: MOS masks will have the same orientation on the sky as the corresponding pre-images. In order to minimize the slit losses due to atmospheric dispersion, in the case of pre-imaging the rotator on sky, otherwise called position angle on sky, is not a free parameter. The default value (90) corresponds to an orientation of the field with E to the top and N to the left, in which slits are aligned with the parallactic angle at meridian crossing. For targets between -45<DEC<-5 deg, also a rotator angle of 0 degrees can be used. This also applies to the PILMOS mode. With well justified reasons, users might request to waive these rules.
  • Effect of atmospheric dispersion: As for MOS OBs, the lack of atmospheric dispersion correction places severe limits on the window in which pre-imaging OBs can be successfully executed. In practice the requirements are that both pre-imaging and MOS of the same field must be obtained while the field is plus/minus 3 hours from the meridian for targets between -45<DEC<-5 deg AND a rotator offset angle of 0 deg, or plus/minus 2 hours for a rotator offset angle of 90 deg at all declinations (see airmass constraint). It is the user's responsibility to make sure that the airmass constraints specified in the OBs do not conflict with this operational requirement, i.e. the airmass constraints must be set such that they correspond to +/-3 or +/-2 hours or less. With well justified reasons, users might request to waive this rule.
  • Submission of pre-imaging OBs: ESO will make every possible effort to execute all pre-imaging as early as possible, and will release pre-images immediately. In effect all pre-imaging OBs will be treated as "carry-under OBs'', meaning that they will be executed as soon as they are ready, even if that is before the period starts. For the Phase 2 proposers this means that it is important to submit pre-imaging OBs as soon as possible, even long before the deadline. The earlier valid OBs are submitted, the earlier the pre-images will be taken, and the higher the probability that follow-up MOS observations will be completed within the narrow window of opportunity.
  • Guide Star for (pre-)imaging: Due to the large Field-of-View of VIMOS the selection of a guide star with the Unified GuideCam Tool is mandatory. Please consider that the guide star used during pre-imaging will be automatically used also for the follow-up MOS observations.
  • Photometric standard: pre-imaging users are requested to indicate in the Readme file whether they need a photometric standard taken in the same night.
  • Containers: pre-imaging OBs cannot be put into concatenation containers. The reason is that Observatory staff needs the flexibility to observe short pre-imaging OBs whenever there occurrs an opportunity in the schedule, in particular at the end of the night.

Specific Requirements for VIMOS Imaging

Here are listed the requirements for pure imaging programmes that are different from the pre-imaging requirements:

  • Observation Category SCIENCE: The 'Observation Category' entry field must be set to SCIENCE in the observation template (VIMOS_img_obs_Offset).
  • Rotator on sky: The rotator on sky, otherwise called position angle on sky, can be set to any value for pure imaging programmes, i.e. without immediate spectroscopic follow-up.
  • Size of offsets and guide stars: Experience with VIMOS operations has shown that, as a rule, imaging observations involving cumulative offsets greater than about 30 arcsec often result in significant vignetting of the field by the guide probe. For this reason, all dither points for offset patterns used in imaging OBs must fit inside a box of size 30 by 30 arcsec. Should a larger offset pattern be needed, users are requested to use separate OBs for the offset positions, using an appropriate guide star for each of the OBs.
    If you have a well justified reason to wish to override the limit on the 30 arcsec offset box within a single OB, then you may submit a Phase 2 Waiver Request. Note that this will mean additional overheads due to acquisition of new guide stars.

Specific Requirements for MOS

  • VMMPS: The VIMOS Mask Preparation Software: The VIMOS Mask Preparation Software (VMMPS) must be used to generate the configuration files that specify target acquisition and mask manufacture for MOS observations (ADP files).
  • Critical: never manually edit the ADP files produced by VMMPS!
  • Critical: never use an old version of the VMMPS software!
  • Relative Astrometric Accuracy Requirements: The mask preparation with VMMPS requires the use of both input catalogues and pre-images. Highly accurate relative astrometry is required for the MOS mode, in the sense that the object positions in the input catalogue must be known relative to those of reference stars in the field of view to better than 1/6 of the slit widths all over the field of view. The pre-image is, then, used to link the astrometric solution of the input catalogue to the VIMOS FOV. Therefore, pre-images taken with VIMOS are mandatory for VIMOS MOS mode observations.
  • OB target coordinates: For the VIMOS_acq_mos_Mask template the target coordinates are automatically loaded in the OB through the mask definition files (ADP files).
  • Submission of MOS OBs: Because of the limitations of airmass constraints MOS OBs must be submitted soon after Pre-Imaging is obtained. To be ready for fast preparation of MOS OBs we recommend the users to download the VMMPS software and test its functionality well ahead of the pre-image release. Important information specifically on the rules for submission of follow-up MOS OBs is available. MOS OBs only need to be submitted after pre-imaging is received (no dummy MOS OBs should be submitted at the general Phase 2 deadline).

Specific Requirements for PILMOS

  • PILMOS: The Unified GuideCam Tool, which includes the former PILMOS tool has to be used to create fake PILMOS (pre-)images and VIMOS catalogues based on a user-provided catalogue. It is mandatory to keep the string 'pilmos' in the file names of those output images and catalogues.
  • VMMPS: The VIMOS Mask Preparation Software: The VIMOS Mask Preparation Software (VMMPS) must be used with the PILMOS output images and catalogues as input to generate the configuration files that specify target acquisition and mask manufacture for MOS observations (ADP files).
  • Critical: never manually edit the ADP files produced by VMMPS!
  • Critical: never use an old version of the VMMPS software!
  • Relative Astrometric Accuracy Requirements: The targets in the user-provided input catalogue should have a relative astrometry accuracy of +/-0.2". Also the astrometric accuracy relative to the reference stars as well as to the catalogue used for the guide star should be less than +/-0.2".
  • Slit Requirement: Currently, PILMOS can only be used for slit widths >=1.0 arcsec.

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