Commensal Observing

Commensal observations can be an effective way to maximize observing hours on Observatory telescopes, by allowing multiple experiments or systems to run simultaneously, when resources allow. The Observatory may support two kinds of commensal observing: commensal observing projects, and commensal systems.

Commensal observing projects refer to peer-reviewed, PI science projects which can be done simultaneously on Observatory telescopes using Observatory backends to conduct two different experiments concurrently. Investigators wishing to carry out commensal observing projects submit independent science proposals as separate primary and secondary proposals, which go through the normal time allocation processes, and are subject to standard data policies.

Commensal systems may be backends or data pipelines which have been approved to run on Observatory telescopes while some PI science experiments are running. Commensal observing systems which are currently on the VLA are described at the proposing page.

A primary proposal controls the telescope pointings and requests the full amount of telescope hours required to fulfill the science objectives detailed in the proposal. Secondary proposals are to run commensally with the primary pointings but make no formal request for an allocation of telescope time. However, when preparing a secondary commensal proposal, please ensure that a nominal amount of time is requested for a session (e.g., 0.1 hrs), even if it is a dummy session. Each proposal must contain estimates of the full resources needed (correlator setup, data rates, etc.) to carry out their specific part of the project.

During the proposal review and time allocation process it will be determined if the combination of the observing set-up and the positions by the primary or secondary proposals conflict with any approved projects. In the case of a conflict, some data restrictions may be applied to the primary and/or the secondary commensal proposal. If the primary and secondary proposals use the same back-end resources (e.g., VLA-WIDAR) it may be necessary for technical reasons to require that the investigators on both primary and commensal projects be given full access to all data.

The Observatory wishes to ensure that peer-reviewed, open-skies PI science projects which are approved via review processes are protected, and that ownership of data is defined. The concept of a “PI science project” includes the science goals and the data produced from PI-specified observing setups. The operation of all commensal systems on Observatory telescopes is subject to the below policy:

Peer-reviewed, open-skies PI science, and the associated output from standard observatory backends, take priority over commensal observing systems. Commensal observing systems may run at all times during open-skies PI science, except when they conflict directly with such science, or cannot run because of technical incompatibility. Conflict is defined by a commensal system reproducing, or being able to reproduce, any part of the PI data approved by the Observatory’s Telescope Time Allocation Committee. The Observatory requires that all commensal systems provide sufficient technical information so that determinations can be made as to whether they will conflict with PI science. The primary project science PI may choose to allow a conflicting commensal system to run; in this eventuality, the commensal system may run alongside the PI science project, subject to technical compatibility. The data produced by a commensal system are controlled by the associated commensal project team.

Observatory telescopes and backends are sufficiently flexible in many cases to allow two experiments to run commensally. To the degree that this enhances science return from the telescopes, Observatory wishes to support commensal projects subject to resource and scheduling constraints. The operation of commensal systems during other (non-open-skies) observing time is subject to the details of relevant contracts or agreements. Groups wishing to carry out commensal observations should submit independent science cases as separate primary and secondary proposals.