Commensal observations can be an effective way to maximize observing hours on NRAO 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 NRAO telescopes using NRAO 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.

Further detail on commensal observing projects appears at the proposal opportunities page, as well as under the News & Opportunities link in the current call for proposals.

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

The Observatory wishes to ensure that peer-reviewed, open-skies PI science projects which are approved via community and Observatory 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 NRAO 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 NRAO Time Allocation Committee.  NRAO requires that all commensal systems provide sufficient technical information 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.

The operation of commensal systems during other (non-open-skies) observing time is subject to the details of relevant contracts or agreements.