Proposal submission information for the following three combinations of telescopes are detailed in individual sections below:

• Very Long Baseline Array (VLBA) and High Sensitivity Array (HSA) proposals requesting time in Semester 2019B (2019 August  1 - 2020 January 31) or multi-semester proposals.
• Global mm VLBI Array (GMVA) proposals for 2019 Session II (Oct 03 - Oct 08), or later sessions.

VLBA Proposals

The VLBA provides ultra-high angular resolution for astrophysical studies including:

• Non-thermal continuum emission, including polarimetry, from active galactic nuclei (AGN), Galactic micro-quasars, pulsars, and other sources.
• Maser emission lines of OH (1.7 and 6.0 GHz), CH₃OH (6.7 and 12.2 GHz), H₂O (22 GHz), SiO (43 and 86 GHz) and other molecules, and numerous thermal absorption lines, in a variety of Galactic and extragalatic circumstances.
• Multiple-phase-center surveys across the primary beam.
• Parallax and proper motion via differential astrometry of a variety of stars, star-forming regions, and nearby extragalactic objects, at accuracies as good as 10 microarcsec.
• Absolute astrometry at accuracies of ~200 microarcsec to expand the International Celestial Reference Frame.

Overall information about the VLBA is available in the VLBA Observational Status Summary (OSS); specific sections relevant to various proposal types are linked below.

The VLBA operates two data systems, a Polyphase Filterbank (PFB), and a Digital Downconverter (DDC).  These are described in detail in Section 5.4 of the VLBA OSS, which also includes suggestions for selecting the optimal observing system for various scientific goals.

Approximately 1000 to 1200 hours of VLBA observing time are expected to be available for Open Skies in observing semester 2019B.  We expect that this available time will be distributed roughly uniformly with  GST.

VLBA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services.  Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database.

Proposals requiring significant additional correlator resources, such as multiple phase centers per field or multiple pulsar phase bins, should consider mechanisms to support the correlation without adversely affecting the throughput of other projects.  These should be entered in the technical justification section of the proposal.

VLBA Shared Risk Observing

In 2019B, the VLBA will again offer the use of all VLBA stations (not the HSA) with a maximum recording rate of 4096 Mbps.  This resource will be offered as Shared Risk Observing. This means that if there is a problem with using this resource, we will not automatically re-observe a given project.  During semester 19B we expect to be able to support 4096 Mbps recording for ~40% of the open-skies observing time.  Therefore we will allocate 4096 Mbps to the most highly-ranked proposals that request it.  Your proposal should indicate whether it could be considered for allocation at 2048 Mbps, perhaps with an increased time request, or dropped from consideration altogether.

VLBA Resident Shared Risk Observing

The VLBA Resident Shared Risk Observing (RSRO) program provides users with early access to new capabilities in exchange for a period of residency in Socorro to help commission those capabilities. For example, the phased-VLA system was developed through RSRO programs.  Users are encouraged to conceive and propose innovative ideas for new VLBA capabilities.  Some staff suggestions are  included at the VLBA RSRO program page, along with details for submitting RSRO proposals.

Proposers should be aware that RSRO capabilities are generally not approved at priority A, owing to the level of risk associated with these observations.

High Sensitivity Array (HSA) Proposals

The HSA comprises the VLBA, phased VLA, GBT, Effelsberg, and Arecibo telescopes.   All of the HSA stations are equipped with instrumentation compatible with the VLBA observing capabilities described in Section 5.4 of the VLBA OSS.  Ongoing special considerations for the HSA telescopes are documented in OSS Section 14.2; new features and special cases are cited here.

VLBI observations combining the VLBA with any one or more of the other four HSA stations can be requested in a single HSA proposal.  However, separate proposals must be submitted for any non-VLBI use of any requested telescopes.

HSA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services.  Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database.  The inclusion of HSA stations should be quantitatively justified in the proposal.

• The phased Very Large Array (Y27) will be available for HSA observing in Semester 2019B, in the A and D configurations.  High frequencies (at receiver bands 22 GHz and above) have better phasing in the more compact configurations (C and D).  High frequency phasing in the extended configurations in the summer can be quite difficult.

Observing with a single VLA antenna (Y1) in conjunction with the VLBA will only be available through the VLBA Resident Shared Risk Observing program.

• The Green Bank Telescope, has transitioned into a new partnership arrangement, the Green Bank Observatory (GBO).  Time available for VLBI on the GBT will be reduced compared to earlier years, and only the most highly rated proposals across all GBT observation types will be awarded time.  Additionally, proposers should be aware that long scheduling blocks (more than 6 hours) will be very difficult to schedule owing to constraints coming from non-NSF GBO partners.  Proposers are encouraged to make clear in the technical justification section any constraints about how observing time could be broken into smaller pieces without adversely affecting the proposed science; include information as relevant regarding maximum elapsed time of a split schedule and minimum scheduling block lengths.

Observations using the GBT 6-cm receiver as part of the HSA must be taken, correlated, and calibrated in full Stokes mode.  Due to the large cross-talk between polarizations, only total intensity (Stokes I) data will be usable. 

• The Effelsberg telescope supports both the PFB and DDC observing systems available on the VLBA.

• The Arecibo 305-m telescope is currently available only with the PFB observing system.  An RSRO project is encouraged to help qualify the 4-channel DDC observing system at Arecibo.

Global 3mm VLBI Array (GMVA) Proposals, including Phased ALMA

GMVA proposals submitted by the 2019 February 1 deadline will be considered for scheduling in 2019 Session II  (Oct 03 - Oct 08), or later sessions.

Complete information on the GMVA is available at the GMVA website.  Ongoing special considerations for the GMVA are documented in Section 14.3 of the VLBA OSS; new features and/or special cases are cited here.

As noted in the HSA section above, GBT time available for VLBI has been reduced due to its new partnership arrangements.

GMVA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services.  Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database.  The inclusion of the GBT and/or ALMA in a GMVA proposal should be quantitatively justified.  ALMA and/or the KVN must be specified by entering "ALMA" or "KVN" as "Other" entries in the PST.

Note that the availability of NOEMA (PLATEAU DE BURE) for GMVA Session II in 2019 and later sessions is currently uncertain.

Another opportunity to propose VLBI observations using the phased ALMA telescope will be available at this Call for GMVA proposals:

It is expected that phased ALMA will participate in some GMVA observations during ALMA Cycle 7 (Oct 2019 - Sept 2020;  see the ALMA Cycle 7 Pre-announcement).   There are likely to be ~43 ALMA antennas available to the ALMA observation; but the phased sum used for VLBI may be constructed only from those that lie within a circle of radius 0.5 km.   GMVA session dates for 2020 are not yet fixed but Session I in 2020, which is traditionally in the period March - May, would provide an opportunity for  GMVA + ALMA observing. 

Any GMVA proposal requesting phased ALMA during Cycle 7 must be submitted via the NRAO PST at the February 1, 2019 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 7 proposals on April 17, 2019.  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 7:

• GMVA observations with ALMA will be limited to a fixed recording mode, which currently provides 2 Gbps on all baselines.  The KVN will not be available in this mode.  Only VLBA telescopes will be available at 7mm in this mode.
• Due to the need to phase up on science target sources themselves, they will be restricted to those with a flux density >0.5 Jy contained within an unresolved core on ALMA baselines up to 1 km.
• In order to make a clean linear-to-circular polarization 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 7 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.

 Resubmission of ALMA Cycle 6 proposals:

The outcome of scheduled GMVA+ALMA Cycle 6 observations scheduled in April 2019 is unlikely to be known until after the ALMA Cycle 7 proposal deadline.  If the PI wishes to mitigate against the possibility that these observations are not completed successfully, the proposal must be resubmitted to ALMA by the Cycle 7 proposal deadline and undergo a new review. The proposal does not need to be resubmitted to the GMVA in this case.  Observations in Cycle 7 will only occur if the April 2019 observations are not completed successfully and the ALMA Cycle 7 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 2019 observations are successful, a new proposal must be submitted to both the GMVA and ALMA by their respective proposal deadlines.