Table of Content

• How the OPC works
• The OPC and the VLT
• Hints for successful applicants
  • General remarks
  • Scientific justification
  • Points of interest
• Concluding remarks

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How the OPC works

The function of the "Observing Programmes Committee" (OPC) is to review and rank the observing proposals for the use of ESO facilities and, thereby, to advise the Director General on the distribution of observing time.

The OPC consists of members nominated by the respective national Committees and of "members-at-large" nominated by the Director General in consultation with the OPC Chairman. The increase in the capabilities of the ESO facilities over the years has led to a substantial increase in the number of (good) proposals, and the OPC has adapted its structure and working procedures accordingly. An adequate number of discipline-oriented sub-committees (panels) has thus been appointed by the Director General to ensure a proper reviewing of the observing proposals submitted by the community. There are currently seven panels. Each panel consists of one or two OPC representatives and of "expert advisers" selected by the Director General in consultation with the OPC Chairman. The chair of the panels rotates between the OPC representatives only.

The current time-allocation procedure is carried out in three steps. A first ranking is made based on the grades given by three panel members who act as referees. During the panel meeting all proposals are then discussed in detail by all panel members and are ranked for each telescope separately. Third, while strictly respecting the ranking assigned by the various panels, the OPC finally adjusts the time allocated to each panel, i.e. the "cut-off" line, which was defined in a preliminary way taking into account the typical amount of time allocated to the panel during previous periods and various constraints on a particular telescope (test time, key programmes, guaranteed time), which may change from one period to another. First, each panel chair reports on the particular situation in his/her panel and requests a new time allocation for the panel, which may be induced by the large number of high-quality proposals, sometimes triggered by new instrumentation. If a consensus cannot be reached on a modified time allocation per panel, then the scientific merit of the proposals near the cut-off line is specifically discussed and the final decision involves a voting of the full OPC.

The advantage of the panel system clearly is that all proposals are discussed and ranked by experts in the field. Furthermore, the adjustment of the time allocated per panel and per telescope made by the OPC, together with an inter-comparison of the scientific merit of proposals in different panels near the cut-off line, provides the flexibility required by the dynamics of our science, all the more important since the implementation of a new instrument can drastically change the potential of a particular telescope. Finally, to average out the unavoidable effects induced by the individual bias of panel membership, the terms of the panel and OPC members are limited to two and three years, respectively. ESO puts particular emphasis on involving young scientists in the panel work.

The final recommendation for time allocation is prepared by the OPC under the guidance of the OPC Chairman. It should be noted that small adjustments are always dictated by scheduling constraints.

The OPC and the VLT

With the advent of the VLT, the OPC enters a new era. In order to be ready for the unanticipated, a full week has been reserved for the OPC and panel meetings for Period 63. All the OPC members will have read the VLT proposals for all panels. The meeting will start with a full OPC meeting where a first evaluation will be made in order to better define the time allocated to each panel for the VLT-UT1. It is our expectation that the proposed science will be innovative, and it is clear that the first two VLT instruments, FORS1 and ISAAC, do not cover the fields addressed by the different panels in a homogeneous way.

The proposal selection for the VLT will to a large extent be dictated by the innovative and ambitious, even risky, character of the science, i.e. these proposals that exploit in the most intelligent way the capabilities of the instrumentation for exploring new frontiers will be favoured. It is probable that some of these proposals will require substantial amounts of observing time; in this case the capacity of the group or consortium introducing the proposal for handling the huge data flow will be critically assessed.

It is important that the applicants thoroughly read the "VLT Science Policy" document endorsed by the STC and the OPC, and approved by Council.

Hints for successful applicant

The view of observing proposals from the standpoint of panel and/or OPC members is sometimes strikingly different from the point of view of the proposers. In what follows, Professor Frank Verbunt (Utrecht), who served in the OPC during the transition period from the "old" to the "new" (i.e. panel) system, describes aspects of this different perspective, in the hope that this may assist prospective users of ESO telescopes in their preparation of observing proposals.

General remarks

The amount of time requested at ESO is always in excess - often by a large factor - of the time available at the telescopes. This implies that it is not sufficient for an observing proposal to be merely good. To be successful, a proposal must be better than many - often most - other proposals. The author of a proposal should realize this, and try to produce the best possible arguments. The members of the panels must make their decisions in a limited amount of time, and based on a limited amount of information. It is incumbent on the proposer to provide the panel with as much relevant information as possible, proposer to provide the panel with as much relevant information as possible, in a form which can be digested rapidly. Write clearly and concisely. Check that the order of the text follows the logic of the proposal. Make sparing use of emphasis, bold face, and exclamation marks.

Scientific justification

A possible structure of an observing proposal is as follows. The first few sentences sketch the general area in which the proposal belongs, and the important questions of current research in this area. As the panel members will be knowledgeable in this area, this sketch can be very brief, and should serve mainly to indicate to the panel the general interest of the proposer in his/her field. For example, if you write a proposal on M dwarfs, X-ray binaries, or an S0 galaxy, you may safely assume that the panel members know what these are, but you should indicate what you think are the important questions that current research on M dwarfs, X-ray binaries, or S0 galaxies tries to answer.

The second part of the proposal zooms in on the specific subject of the proposed observations. Which specific question do you want to tackle with your proposal? The third part gives a brief non-technical description of the proposed observations (the technical part is addressed later) and explains how these observations answer the goal of the proposal. It is important here to be both specific and realistic. Thus to state that a measurement of the B-V colour of the target will determine the amount of dark matter in the Universe will not impress the panel unless you are able to specify through which steps you can do this. It is this part of the proposal which will to a large extent determine your standing with the panel. A realistic assessment of the expected results will show the panel that your scientific judgment is sound; an exaggerated claim will not.

If the method of analysis and/or interpretation has been described in an article, you may limit yourself to a brief outline, and provide a reference for the full detail. If the article only exists as a preprint, provide a website or an ftp address where the preprint in question can be obtained. The panel should be provided with enough information to assess how reliable your proposed methods are.

Points of interest

When writing a proposal, it is advisable to keep in mind the following points.

• Who will be interested in your results?
  Maybe only the proposer... but maybe all astronomers working on the same object, on the same class of objects, and indeed maybe many astronomers in different fields of interest. It is useful if you assess this in the proposal. The wider the possible interest in your results, the higher the ranking of your proposal.
• Do you have theoretical backup?
  If so, the value of your proposal is enhanced. For example, if your proposal aims to determine the element abundances in an M dwarf or an S0 galaxy, it will be useful if you can show that you have the ability to obtain theoretical line strengths as a function of abundance. If you wish to determine the amount of dark matter in a cluster of galaxies, it helps if you can show that you have simulations which indicate that the proposed data will suffice to do this.
• Are you capable of handling the data?
  An indication of this is always useful; it is mandatory if the data analysis is complicated and not straightforward. The best way to show that you can do the job is to refer to your track record in the form of earlier publications. If this doesn't exist, because you are embarking on a new field, you may wish to propose a pilot study first so as to be able to show your mettle.
• Statistics
  You should show awareness of the statistical aspects of your proposed observations. For example, if ten similar systems have been observed, and you propose to observe number eleven, you must assess how much can be learned from the one new system that hasn't been learned yet from the previous ten. If a hundred systems have been observed, and you propose to observe ten more, you cannot claim that the statistics will be improved dramatically, unless you show that the proposed targets cover a range of parameters that is not well covered by the earlier observations.
• Target selection
  It is useful to explain why you selected your specific target(s). For example, if you wish to determine the amount of dark matter in the galaxy cluster Abell A2218, explain why this cluster is a better target than other clusters. Possible answers to explore include
  • the galaxies in this cluster are bright and can be observed in relatively short exposures
  • many velocities have been measured already, to which your data can be usefully added
  • simulations show that the galaxies in this cluster are well distributed to determine the dark matter distribution
  • the amount of dark matter has already been determined with another method, to which our results can be compared usefully.
  • Etc...

Concluding remarks

The OPC procedures outlined above result from experience accumulated over many years by successive generations of delegates. They are continuously evaluated by the OPC itself, by the ESO Directorate and by Council.

It will, however, always remain impossible to define objective criteria for selecting the very best proposals in an unambiguous way. Our consolation is that the wide expertise of the panel members and the high pressure factors on all telescopes guarantee that only proposals that are of a high scientific value are selected.

We hope that the community will conspire to make our task very difficult again, by introducing for Period 63 many high-quality proposals and by being ambitious, in order to fully exploit the unique opportunities offered by VLT-UT1.