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Announcement of 3mm VLBI in Cycle 5

Jan 06, 2017

It is expected that phased ALMA will participate in some GMVA observations during ALMA Cycle 5 (Oct 1 2017 - Sept 30 2018; see the ALMA Cycle 5 Pre-announcement). The number of ALMA dishes possible in the phased array is likely to be 35 - 43 (but see below). ALMA will not be in a configuration suitable for VLBI during GMVA Session II 2017. GMVA session dates during Cycle 5 are not yet fixed, but Session I in 2018, which is likely to be in March or April, should provide an opportunity for GMVA + ALMA observing. GMVA Session II in Fall 2018 may also overlap with ALMA Cycle 5 in a configuration suitable for VLBI.

Any GMVA proposal requesting phased ALMA during Cycle 5 must be submitted via the NRAO PST at the February 1, 2017 deadline.

Proposers should:

  • specify "ALMA" in the Other Stations text field in the PST
  • select the default GMVA 3mm observing mode of 2 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 also be submitted at the deadline for ALMA Cycle 5 proposals in April 2017. For this, all proposers (PI and Co-I's) must be registered ALMA users (see:


Restrictions on GMVA+ALMA proposal in Cycle 5:

  • GMVA observations with ALMA will be limited to a fixed, continuum-only, mode, which will provide 2 Gbps on all baselines. The KVN will not be available in this mode.
  • Due to the need to phase up on the target source, only sources with correlated flux densities >0.5 Jy in intra-ALMA baselines out to 1 km may  be proposed for observation. Only ALMA antennas within the 1 km radius will be part of the phased sum.
  • In order to make a clean linear-to-circular transformation of ALMA recordings, any target source must be observed for a duration of at least 3 
    hours (breaks for calibrators permitted) to sample a range of parallactic angles.
  • Large Programs (>50 hours of observing time) are not permitted because phased ALMA is a non-standard mode.
  • No long-term (i.e., multi-cycle) programs may be proposed, and no proposals will be carried over into the next cycle.
  • There is a cap for VLBI of 5% of ALMA Cycle 5 observing time. As time for GMVA observations will thus be scarce, proposals should include a
    justification as to why ALMA is essential for the goals of the project.


Resubmission of ALMA Cycle 4 proposals:

The outcome of scheduled GMVA+ALMA Cycle 4 observations in April 2017 is unlikely to be known until after the ALMA Cycle 5 proposal deadline. If the PI of awarded GMVA+ALMA Cycle 4 time wishes to mitigate against the possibility that these observations are not completed successfully, the proposal must be resubmitted to ALMA by the Cycle 5 proposal deadline and undergo a new review. The proposal does not need to be resubmitted to the GMVA in this case. Observations in Cycle 5 will only occur if the April 2017 observations are not completed successfully and the ALMA Cycle 5 proposal is ranked high enough for scheduling.

However, if the PI wishes to obtain a second epoch of GMVA+ALMA observations, even if the April 2017 observations are successful, a new proposal must be submitted to both the GMVA and ALMA by their respective proposal deadlines.

Any questions about the VLBI prospects for ALMA in Cycle 4 should be directed to the ALMA Helpdesk: Additional information on using ALMA with the GMVA can be found at the websites for the Long Baseline Observatory ( and the GMVA (