Applications for Use of Visitor Instruments at the VLTI

The possibility to have Visitor Instruments at the VLTI has been granted to permit innovative observations by team susing stand-alone instruments, free from a substantial fraction of the requirements for fully automated VLTI general use instruments. In addition, the Visitor Instruments could provide a powerful scientific/technical test bench for new instrumental concepts, eventually to be incorporated later in VLTI facility instruments. The set of guidelines on how to propose and carry out this type of observation is given below. For technical information concerning the interface between a Visitor Instrument and the VLTI please follow this link.

Interested parties should contact the VLTI Programme Scientist (A. Mérand), Paranal Instrumentation Programme Manager  (L.Pasquini) and Paranal director (A. Kaufer).

As of July 2021, ESO kindly requests that prospective applicants contact the ESO Director for Science at least 3 months before submission to funding sources.  Implementation cannot be guaranteed if funding for such projects is obtained without a green light from ESO.

Guidelines for VLTI Visitor Instruments

Scientific Requirements

Acceptable Visitor Instruments (VI) shall offer observational capabilities not covered by other VLTI instruments, or a largely superior performance in at least one valuable and sufficiently extensive scientific application. A major advantage of a VI is the capability to react quickly to new scientific and/or technical opportunities. Speed shall be a major criterion for the selection of VIs.

Technical Requirements

VIs shall be fully stand-alone, complete instruments, including their own data acquisition and storage capabilities. VIs shall comply with the VLT standards for safety, the interface to the VLTI Facility, power and coolant supplies, and LAN connection. Detailed information is available here.

Operation Mode

VIs shall be operated exclusively in Visitor Mode. The use of Observation Blocks is optional.

Data Flow and Archiving

VI data shall not enter the VLT data flow system. The VI Team shall take care of storing the data.


Proposals for a visitor instrument may be submitted at any time by individual institutes in ESO member states and Chile, Consortia of such institutes or international Consortia led by an ESO member state institute.

Procedures for the Approval of VI Proposals

VI proposals shall be submitted to ESO where they will be evaluated scientifically, technically, and operationally. Proposals shall contain

  • a broad scientific justification,
  • a thorough technical description of the instrument,
  • a thorough description of its operation,
  • the number of nights required for commissioning,
  • a detailed list of resources (manpower, technical) required from ESO,
  • a scientific Observation Proposal of the VI Team, specifying the number of nights requested and their distribution through the ESO Observing Periods.

The proposals along with their ESO evaluation will be presented jointly to the STC and OPC. The STC will give its recommendations concerning the scientific and technical value of the proposed VI. The OPC will give its recommendations concerning the number of VLTI nights to be granted to the VI Team.

VI Contract

Following positive OPC and STC recommendations, a contract shall be negotiated and stipulated between ESO and the VI Team. The contract shall specify the performance requirements of the instrument, the periods during which it will be attached to the telescope, the operational procedures, as well as the number and distribution of the observing nights allocated to the VI Team. The VI Team shall be responsible for delivery, installation, commissioning and operation of the instrument, as well as for its dismounting from the VLTI at the end of the contract. The contract may be extended by mutual agreement.

Development, design and construction of VIs

ESO shall, where applicable, be kept informed about the progress and status of the instrument during its design and construction phases, e.g. by participating in the design reviews. At the end of the commissioning, the instrument shall be released for operation, upon verification that it meets the requirements specified in the contract.

Use of VIs

After release for operation the VI Team shall be entitled to use the instrument on the VLTI for the amount of time specified in the contract. Any extra-time required for commissioning may be deducted from the scientific time.

Property of VIs

A VI remains property of the VI Team, unless differently agreed upon between ESO and the Team.