Joint VLT/I-ALMA proposals


With the aim of taking full advantage of the complementarity of optical-NIR and sub-millimetre observing facilities, ESO and ALMA have entered into a Joint Proposal agreement, to enable those science cases that require observations with both ALMA and VLT/I telescopes to have their goals fulfilled.

In this framework, Joint VLT/I-ALMA Proposals will be offered as of Period 112 and ALMA Cycle 10 (see the ESO call published on February 28, 2023.) By agreement with the ALMA Observatory, ESO may award a maximum of 50 hours of ALMA observing time on each of its arrays to Joint Proposals per year. Similarly, ALMA will be able to allocate up to 50 hours per cycle on the VLT/I in the yearly ALMA Call for Proposals.

Selecting the leading facility

As a general rule, a Joint Proposal should be submitted to the facility providing the data which are most relevant for the specific science case. It is expected that this typically translates to the amount of requested time, although there may be gray areas. One aspect the PIs may want to consider, which is related to the core of the science case, is the desired expertise of the reviewers, which is typically optical/NIR-oriented for VLTI/I and millimetre-oriented for ALMA.

In case of doubts, the prospective applicants can consult with ESO or ALMA Helpdesks.

ESO proposals requesting ALMA time


  • Joint proposals requesting ALMA time will comply with both ESO and ALMA Users' Policies and Call for Proposals guidelines. 
  • ESO may allocate up to 50 hours of ALMA time per yearly Cycle on each of the ALMA Arrays (i.e. 12-m, 7m, and TP). 
  • Joint Proposals submitted to ESO cannot request ALMA time for VLBI or phased array observing modes. 
  • ALMA Large Programs are not allowed when Joint Proposals are submitted to a partner observatory, and therefore the amount of ALMA time requested must be less than that of the ALMA Large Program threshold (see the ALMA Proposer's Guide for a definition of a Large Program).
  • Only Normal VLT/I-ALMA joint proposals are offered at ESO.
  • When submitting a VLT/I-ALMA joint programme through ESO, the proposing team must include in their scientific rationale a strong justification for the need of both facilities in order to reach the proposed science goals.
  • Joint VLT/I-ALMA proposal will only be approved or rejected for both facilities. Partial approvals will not be considered, as the concept is that the science goals of a joint programme can only be achieved acquiring data with both facilities.


Joint Proposals will be allowed to request array configurations offered between the time the project will enter the ALMA queue (i.e. upon project preparation subsequent to proposal approval as indicated below) until the end of the ongoing ALMA Cycle, as well as those offered in the upcoming ALMA Cycle. During the preparation of the proposal, PIs will use the ALMA Observing Tool to input the technical details and perform a first automatic validation.

Projects requiring observing capabilities offered by ALMA in the upcoming Cycle may not be yet supported by the version of the Observing Tool available on the ALMA science portal. In those cases, the PI will make use of other tools provided by ALMA and provide a detailed explanation of the assumptions made and how the observing time was estimated. PIs are responsible for summarizing the technical specification for the requested ALMA observations; this will be used for initial technical assessment. As indicated in ALMA Proposer's Guide, an incomplete Technical Specification may lead to the rejection of the proposal on technical grounds. The specification will be provided in text format and will contain the information indicated below.

ALMA projects will be evaluated based on the technical feasibility of the requested observations, the scheduling feasibility considering the requested array configuration and time constraints. Upon acceptance of a Joint Proposal by ESO, PIs will be requested to submit the project with the ALMA Observing Tool. The JAO will perform a final detailed technical assessment and then proceed to prepare the Scheduling Blocks in preparation for observations. In addition to any significant technical issue found during this process, projects that, during preparation of the Scheduling Blocks, result in a larger observing time than requested in the proposal ALMA Technical Specification are subject to rejection on technical ground at the discretion of the JAO.

Once the Scheduling Blocks have been prepared, projects will immediately enter the ALMA observing queue, unless requesting observing capabilities only offered in the upcoming Cycle. In that case the project will enter the queue at the corresponding Cycle start date. As such, since Joint Proposals is a mode offered for ALMA Cycle 10, proposals accepted during ALMA Cycle 9 will only enter the queue at the Cycle 10 start, on October 1st 2023. As a consequence a Joint Proposal will only be able to request array configurations offered for ALMA Cycle 10. Projects will remain in the ALMA queue up to a total period of two years.


ALMA Technical Specification

PIs applying for joint VLT/I-ALMA proposals will have to provide a Technical Specification for the ALMA part when submitting their proposal via the ESO p1 interface. The technical specification will be provided uploading a PDF document produced from an ad-hoc template. The template will be made available to the user directly from the p1 interface. A fac-simile of the template is shown below. More details on the preparation and upload process are given in this presentation


Number of sources:

Mapping area: (Single Pointing/Multiple pointings/Rectangular Mosaic of given area)

Required 12 m Array configuration(s):

Time request considering overheads (Times calculated with Observing Tool already include overheads)

12 m Array:

7 m Array:


Requested Band(s):

Representative sensitivity for reference array (i.e. 12m, or 7m for ACA stand-alone projects) and aggregated bandwidth used for sensitivity calculation:

Is the time request resulting from OT: (Yes/No)

If No, indicate how the time was estimated:

Report here the highest spectral and imaging signal-to-noise ratios expected in your sample:

Is there any time constraint, including simultaneous or coordinated observations involving multiple observatories?:

Is full-polarization required? (Yes/No)

If so, report here:

  • the coordinates of any source with a declination northern than +30deg:
  • the expected source linear/circular polarization fraction:


General Technical Justification:

This must include Sensitivity, Imaging parameters, Correlator configuration, and any other justification requested by the OT (extra text boxes in the technical justification section.

List of OT messages:

This must include any blue message reported by OT at the top of the Technical Justification section and any warning/error message when validating the project:

(Exclude obvious errors, like missing title/abstract/scientific justification, which are not= required for the purpose of technical justification)


Proposal preparation

Joint VLT/I-ALMA Proposals are prepared and submitted using the p1 interface, like for all other programme types offered by ESO. An introduction to the ESO p1 system can be found here. Please note that for accessing the interface you need to have a valid ESO User Portal account.

Details on the aspects related to the specific case of the Joint Proposals can be found in this presentation.


Review and allocation process

Joint VLT/I-ALMA proposals will be reviewed by the ESO OPC together with the regular ESO proposals. The ALMA Technical Specification will forwarded in parallel by ESO to ALMA for the feasibility assessment of the ALMA part.

In case of approval and no technical issues, the succesful PIs will be contacted and asked to submit a proper proposal through the ALMA system.

Important note: Joint Programmes are either fully approved or fully rejected. No partial approval or rejection will be considered, as the concept behind the Joint Programmes is that the usage of both facilities is vital to achieve the final science goal. If this is not the case, applicants may consider submitting separate programmes to the two facilities.

The scheduling and the preparation of the observations will then proceed independently for the two facilities, which will coordinate the execution matching possible time constraints for the joint observations.

Any questions on Joint Proposals can be directed to the ESO or ALMA Helpdesks.

Last updated: Fri Feb 28 08:36:56 CET 2023