Science Highlight




Participation of ALMA in GMVA observations in ALMA Cycle 4

It is expected that phased ALMA will participate in some GMVA observations during ALMA Cycle 4 at 3mm wavelengths (Oct 1 2016 - Sept 30 2017; see the ALMA Cycle 4 Pre-announcement). The number of ALMA dishes in the phased array is likely to be 30 - 40. ALMA will not be in a configuration suitable for VLBI during GMVA Session II 2016. GMVA session dates during Cycle 4 are not yet fixed but Session I in 2017, which is likely to be in March or April, should provide an opportunity for GMVA + ALMA observing. (GMVA Session II in 2017 is unlikely to overlap in Cycle 4 with ALMA in a configuration suitable for VLBI.)

Any GMVA proposal requesting phased ALMA during Cycle 4 must be submitted via the NRAO Proposal Submission Tool (PST) at the February 1, 2016 deadline at NRAO Interactive Services. Use of the PST requires registration in the NRAO User Database.

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 (although a different implementation of this will actually be used)
  • 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 4 proposals in April 2016. For this, all proposers (PI and Co-I's) must be registered ALMA users (see: http://www.almascience.org).

Restrictions on GMVA+ALMA proposal in Cycle 4:

  • GMVA observations with ALMA will be limited to a fixed, continuum-only, mode, which will provide 2 Gbps on all baselines (except those to Plateau de Bure and the KVN).
  • 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. (This limit is set by the current state of testing of the phasing system).
  • 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 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 4 observing time. As time for GMVA observations will thus be scarce, proposals should include a quantitative justification as to why ALMA is essential for the goals of the project.

Any questions about the VLBI prospects for ALMA in Cycle 4 should be directed to the ALMA Helpdesk: http://help.almascience.org. A similar news item will be distributed announcing the call for 1mm VLBI observations through the Event Horizon Telescope Consortium (EHTC) by the beginning of February 2016.