Global VLBI at mm wavelengths including ALMA

(ALMA Cycle 11, October 2024 - September 2025)

Since Cycle 4, ALMA participates in Very Long Baseline Interferometry (VLBI) at millimeter wavelengths. The observations at 7mm and 3mm (ALMA Bands 1 and 3) are performed as part of the Global Millimeter VLBI Array (GMVA). For observations at 1mm and 0.8mm (ALMA Bands 6 and 7), ALMA joins the Event Horizon Telescope (EHT) network. The first PI-led mmVLBI observations including ALMA took place in spring 2017. Since Cycle 10, spectral line capabilities are offered for GMVA+ALMA observations in both wavelengths. The frequency ranges of individual GMVA stations can be found in the Technical Guidelines of the GMVA.

Proposal preparation

 The phased ALMA is expected to participate in some GMVA and EHT observations during ALMA Cycle 11 (October 2024 - September 2025), likely in late April 2025.

Please note carefully the difference in proposing procedures and proposal deadlines:

GMVA + ALMA

Proposals requesting mmVLBI observations at 7mm or 3mm have to be submitted both via the PST and the ALMA-OT. In the PST, proposers should
  • specify "ALMA" in the text field "Other Stations"
  • select the default GMVA observing mode of 4 Gbps, dual polarization
  • specify the amount of time and GST range(s) needed for ALMA separately, either in Session Constraints or Comments, or in the Technical Justification.
A separate proposal to ALMA must be submitted via the ALMA-OT before the deadline for ALMA Cycle 11 proposals in April 2024. Please note that the PI and all Co-Is must the registered ALMA users and that the proposal text submitted via the ALMA-OT must conform to the guidelines for the dual-anonymous refereeing process. The text submitted via the ALMA-OT and via the PST need not be identical, but the overall scientific justification must be the same. Please note that the PI and all Co-Is must be registered ALMA users.

Detailed information on how to propose for mmVLBI will be published on the ESO Science Portal together with the Call for Proposals. The details for GMVA+ALMA proposals can already be found at the GMVA Call for Proposals. In addition, the ARC nodes, e.g. the German ARC node, Allegro (Dutch node) and the Italian ARC node, offer support at all stages of an ALMA observing project and interactive training opportunities.

EHT + ALMA

Information about how to propose for EHT+ALMA observations will be given in the ALMA Call for Proposals in March 2024. The proposal to ALMA must be submitted via the ALMA-OT before the deadline for ALMA Cycle 11 proposals in April 2024. Please note that the PI and all Co-Is must the registered ALMA users and that the proposal text must conform to the guidelines for the dual-anonymous refereeing process.

Detailed information on how to propose will be published on the ESO Science Portal together with the Call for Proposals. In addition, the German ARC node and Allegro (Dutch node) offer support at all stages of an ALMA observing project and interactive training opportunities.



Scheduling and Observations

 The scheduling of mmVLBI observations is NOT done by the proposers themselves, but by a team of mmVLBI experts from the VLBI network providers and the Joint ALMA Office (JAO). Besides maximizing the scientific output in the scheduled time slots by interleaving the different approved projects, the team also inserts all the necessary calibrators at appropriate intervals into the schedule. Any special requirements or requests regarding the scheduling of approved mmVLBI projects should be directed to the contact scientist (CS) of that project.

In Cycle 11, observations are foreseen be taken in campaign mode at pre-defined dates during the GMVA Session 2025/I (usually scheduled in the period March to May). At least 43 ALMA antennas are expected to be available in Cycle 11, but the phased sum used for VLBI will be formed only from those that lie within a circle of radius 0.5 km (or less, depending on atmospheric conditions). PIs of approved mmVLBI proposals should be prepared to provide additional information and feedback to the expert team in the weeks leading up to the mmVLBI campaign(s).

After the observations, the disk packs containing the recorded VLBI data are shipped from the stations to the correlation centers at the MPIfR in Bonn, Germany, and at MIT-Haystack, USA. Please note that the shipment of disk packs usually takes several weeks. The South Pole station closes for winter. Between February and October, there are no flights to or from that station. Hence, the disk packs from the 2024 mmVLBI campaign(s) won't be shipped from that station before November 2024.



Correlation and Data Access

 Correlation of the VLBI data will be performed at the correlation centers at the MPIfR in Bonn, Germany, and at MIT-Haystack, USA. PIs are notified when their correlated data are available for download.

The ALMA-only data, recorded in parallel, will undergo quality assessment and data reduction similar to ALMA data of standard observing modes. PIs are notified of the availability of their data by email. They can then download their data from the ALMA archive. The proprietary period for the ALMA-only data is one year, starting on the day of the notification email.



Data Reduction

 Like VLBI data at lower frequencies, correlated mmVLBI data can be reduced in AIPS, which offers a rich suite of VLBI tasks. Basic VLBI data reduction capabilities like a finge fitting procedure have been implemented in the latest CASA releases as well. The lectures of the 2020 CASA VLBI workshop and the CASA VLBI training workshop in June 2023 offer a detailed introduction on reducing VLBI data with CASA.

The ALMA-only data can be reduced and analyzed as usual using CASA.