Target of Opportunity Procedures

This page describes the procedures to be followed in the preparation, activation, and data retrieval of Target of Opportunity (ToO) programmes both at the VLT and the La Silla telescopes. Please note that further details on policies and procedures are given in the Observatory's webpages.

Phase 2 Submission

The Phase 2 process for ToO programmes follows similar procedures as those of other, regular programmes as described in the Instructions for Phase 2 preparation of Service Mode runs. In particular, the following information must be submitted before the Phase 2 deadline:

  • A set of Observation Blocks (OBs) that completely describes the required observations. The target coordinates should be set to RA=00:00:00.0, Dec=00:00:00. Note that it is not necessary to submit OBs to fill up the entire allocated time: only one complete set of OBs is required. Should a ToO event require the execution of an OB identical to another that was already used for a past observation of the same program, the same OB will be used.

    Note that this is a unique exception in Service Mode procedures applicable exclusively to ToO programmes! OBs belonging to any other class of programmes are executed only once.

    Users can also submit multiple sets of OBs to cover different situations (e.g. faint and bright events). In this situation, the submitted OBs can over-subscribe the time allocated to the programme, which will be terminated once the actually executed time equals the allocate time. Again, this is another unique exception in Service mode procedures applicable exclusively to ToO programmes. The set of OBs submitted for any other class of programmes must always keep within the allocated execution time.

    ToO OBs should not be organized in scheduling containers, but rather be loose OBs. In the spirit of ToO observations the same OB can be triggered more than once, and this will not be possible if they are inside a scheduling container.

    The time-critical nature of ToO observations supersedes the conditions specified in the Constraint Set: this means that, once triggered and started, a ToO observation will be considered to have been successfully executed independently of the prevailing seeing and sky transparency. The Constraint Set of the OB must therefore request only the least stringent constraints possible.

    Finally, please be reminded that, as explained in the OB naming conventions, all ToO OBs must have names starting with the prefix TOO_

  • A complete README file. Please pay special attention to the ToO Information section, where any particular instructions for the execution must be clearly explained.

The submission of finding charts is obviously not required, since the targets are not known in advance.

Follow-up observations of ToO targets

This note applies to programs proposing first to discover a given target and then to follow-up the newly discovered target(s) with a specific observing cadence in order to properly characterize it/them. In principle, while the discovering part needs for ToO triggers, the follow-up part does not require ToO triggers, as reported also in the Call for Proposal. Ideally, at Phase-1 and Phase-2 the ToO and non-ToO parts shall be split into separate runs. The non-ToO part shall be a normal A-class Service Mode run and therefore eligible for carry-over. If instead all the observations will be included in a single ToO run please be aware that the standard carryover policy for Target of Opportunity programmes will be applied, which foresees the termination of incomplete ToO runs at the end of the Period.

List of Approved Activators

For security reasons, only the programme Principal Investigator (PI) and people authorized by the PI will be allowed to activate the programme during the course of the Period.

The PI of the ToO programme must include in the corresponding section of the README file a list of people who are authorized to activate their programme, once the Phase 2 submission is completed. This list must contain the following information:

  • Name and e-mail address of the PI
  • List of names and e-mail addresses of all persons the PI grants permission to activate the programme.

Activating ToO Observations

To activate a ToO programme, users should use a dedicated Web-based form. Two such forms exist:

Please make sure that you are using the correct form corresponding to the Observatory where the observations must be performed. This form is designed to make sure that the Observatory receives the complete information package needed to perform the observations. Alerting the Observatory via this Web entry is the first contact, and guarantees a direct line to the support astronomer. The Observatory may contact the activator for further iterations, and will keep the activator up-to-date during the progress of his/her request. In case of submission or network problems, an e-mail message should be sent to either Paranal Science Operations ( or La Silla Science Operations ( activation e-mail message must contain:

  • ESO Programme ID
  • List of available OBs
  • Target coordinates
  • Exposure times (if necessary)
  • A few words about the target and any special requirement (e.g. timing) as well as any other information which is felt to be important for a successful execution of the observations.
  • The name, e-mail, and phone number of a contact person who is prepared to discuss this ToO programme and make decisions about its execution. This person should be available via telephone.
  • One or more finding charts should also be provided, in PostScript format, attached to the activation email. Finding charts should be prepared following the conventions indicated in the instructions for the preparation of Finding Charts for Service Mode Programmes, although in this case they must be submitted separately as PostScript files rather than as a part of the OB.


Note for observations using instrument-specific preparation software: Time-critical observations requiring supplementary files from instrument-specific preparation software (FIMS, VMMPS, NAOS PS, FPOSS) should be a very rare occurrence. In such cases, the relevant configuration files (e.g. .p_targ, .p_focf for FIMS, .aocfg files for NACO...) should sent as a single file attachment (tar file that will also include finding charts in addition to configuration files) through the above linked webform. Alternatively an email attachment by email to Paranal Science Operations ( can also be used. A list of which configuration files should be associated to which OBs should be described in the e-mail. Users should keep in mind that a longer response time from Paranal is to be expected in the case of execution of ToO OBs containing instrument configuration files.

Time accounting

Unlike for normal programmes, the time accounting for ToO programmes is made on the basis of the actual time invested in executing the observation, taking into account all operational overheads, which may include the change of focal station of the telescope. For all other classes of programmes, the overheads charged are those published in the Call for Proposals and the instrument manuals, and computed by P2PP.

Based on this accounting, once a program has used up all its hours, irrespective of the number of triggers executed, no more triggers will be accepted.



Post-execution Process

After ToO OBs have been executed, ToO data will be made available immediately to the PIs and their data delegates through the ESO archive via the User Portal. ToO data delivery via dedicated FTP accounts is discontinued starting from Period 90 (October 1, 2012).


Instrument selector

This page is valid for all instruments