Global VLBI at mm wavelengths including ALMA

(ALMA Cycle 8, October 2020 - September 2021)

Since Cycle 4, ALMA participates in Very Long Baseline Interferometry (VLBI) at millimeter wavelengths. The observations at 3mm are performed as part of the Global Millimeter VLBI Array (GMVA). For observations at 1.3mm, ALMA joins the Event Horizon Telescope (EHT) network. The first PI-led mmVLBI observations including ALMA took place in spring 2017.



Please note that the information below has been compiled in early 2020 in preparation for the original Cycle 8 Call for Proposals. When the new Cycle 8 Call for Proposals will be prepared in early 2021, this webpage will be updated according to the latest information.




New in Cycle 8: Beginning in Cycle 8, mmVLBI proposals can include faint science targets, i.e. sources with a correlated flux density <500 mJy within an unresolved core on ALMA baselines up to 1 km. These observations will be done in passive phasing mode, where it is recommended to have a bright calibrator within 5 degrees of the science target. In addition, the default GMVA 3mm observing mode has been upgraded from 2 Gbps to 4 Gbps.


Proposal preparation

 The phased ALMA is expected to participate in some GMVA and EHT observations during ALMA Cycle 8 (October 2020 - September 2021).

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

GMVA + ALMA

Proposals requesting mmVLBI observations at 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 3mm observing mode (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 8 proposals on 15 April 2020. Please note that the PI and all Co-Is must the registered ALMA users. 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 offers support at all stages of an ALMA observing project and interactive training opportunities, in particular in March/April 2020.

Please refer to the ALMA pre-announcement or the GMVA Call for Proposals for detailed information on resubmissions, capabilities and restrictions for GMVA+ALMA in Cycle 8.

EHT + ALMA

Information about how to propose for EHT+ALMA observations will be given in the ALMA Call for Proposals in March 2020. The proposal to ALMA must be submitted via the ALMA-OT before the deadline for ALMA Cycle 8 proposals on 15 April 2020. Please note that the PI and all Co-Is must the registered ALMA users. 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 offers support at all stages of an ALMA observing project and interactive training opportunities, in particular in March/April 2020.


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 8, observations are foreseen be taken in campaign mode at pre-defined dates during the GMVA Session I 2021 (usually scheduled in the period March to May). There are likely to be 43 ALMA antennas available in Cycle 8, 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 2021 mmVLBI campaign(s) won't be shipped from that station before November 2021.


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 noticifation email.


Data Reduction

 Similar to VLBI data at lower frequencies, correlated mmVLBI data are usually reduced in AIPS, which offers a rich suite of VLBI tasks. Basic VLBI data reduction capabilities like a finge fitting procedure are under development and may be implemented in future CASA releases.

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