The 1 August 2014 deadline applies to all types of Very Long Baseline Array (VLBA) and High Sensitivity Array (HSA) proposals requesting time in semester 2015A (1 February – 31 July 2015), or multi-semester proposals. It also applies to global mm VLBI proposals for the May 2015, or later, sessions. Please see the instructions for submitting VLBA, HSA, and global VLBI proposals. Requests for resources beyond just the VLBA – i.e., the inclusion of HSA or Global 3mm VLBI (GMVA) stations – need to be quantitatively justified in the proposal.

VLBA Observing Capabilities

The VLBA provides ultra-high angular resolution for observations of non-thermal continuum emission, maser 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 absorption-line studies of numerous thermal spectral lines. The VLBA operates two data systems. In the following summary, an "IF" is one of the four 512-MHz signals carried on cables from the antenna's vertex to the control building, and a "channel" refers to a single contiguous frequency range, of any bandwidth, observed in a single polarization, that is sampled, filtered, and recorded as a separate entity. The two data systems comprise the following:

• The Polyphase Filterbank (PFB) observing system provides sixteen 32-MHz channels, with a fixed 2048-Mbps recording rate. The channels can be selected flexibly between two VLBA IF inputs. Channel placement is restricted to 32-MHz steps along the frequency axis.

• The Digital Downconverter (DDC) observing system is considerably more flexible than the PFB. As many as eight channels can be selected arbitrarily from up to four VLBA IFs, and placed at 15.625-kHz steps on the frequency axis with bandwidths ranging from 1 MHz to 128 MHz by factors of 2. Extremely narrow bands can be accommodated by observing at 1 MHz bandwidth and selecting a narrower range using the DiFX correlator's spectral zoom mode. All bandwidths must be identical, and channels cannot span either of two zone boundaries within the IF band, at 640 and 896 MHz. Use of 128 MHz bandwidth is limited to 4 (or fewer) channels by the 2048-Mbps recording rate limitation.

Wideband science is possible using either the PFB observing system, at its fixed 2048 Mbps data rate, or the DDC system at 2048 Mbps or lower rates. Further details are available in the VLBA Observational Status Summary. It is anticipated that the pool of recording media will support the highest data rates for approximately half of all observing hours. Spectroscopic and other narrow-band observations will generally be best supported by the DDC system. Inputs to either data system can come from any of the four VLBA IFs. Typically only two are used, in opposite polarizations, but less common modes are also possible, generally dual-polarization dual-frequency cases. The four-IF capability of the DDC allows these modes to be exploited.

VLBA Filler Project Challenge

NRAO continues to solicit proposals for one or more Large projects for up to 750 hours per semester of "filler" time on the VLBA. To be eligible for this large time allocation with FILLER status the project should be flexible enough to be scheduled:

• under non-ideal weather conditions
• with less than the full complement of antennas
• with a target list of source positions around the sky
• with short duration or variable length scheduling blocks.

Teams must provide tools that allow VLBA operations, with minimal effort, to create schedules for arbitrary blocks of time of one hour or more when such time becomes available during dynamic scheduling. Large proposals for VLBA filler time will be subject to the usual NRAO Large Proposal Policy. Multi-semester proposals will be considered.

Types of projects that might use VLBA filler time include surveys of many sources, astrometry, geodesy, deep integrations spread over many sessions, and long term monitoring. It is rare for fewer than 6 or 7 antennas to be functional and have good observing conditions, so high frequency projects that can use a reduced array are viable. Proposers should be aware that the available time will not be uniformly spread across the sky because of the high demand for Galactic time from high priority programs. Proposals that require much greater correlator resources than typical projects (such as multiple phase centers per field) should address mechanisms to support the correlation without adversely affecting the throughput of other projects.

Regular proposals that can utilize the same sort of VLBA filler time are also encouraged.

VLBA Resident Shared Risk Observing Program

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. A number of additional areas are suggested at the RSRO program page, including the development of Y1 with the VLBA. We encourage other innovative ideas for new VLBA observing modes from the community as well. Details are available on the VLBA RSRO program webpage.

High Sensitivity Array (HSA)

The phased VLA (Y27) will be available for VLBA proposals in semester 2015A, in configurations B/BnA/A. HSA proposals can request the phased VLA in conjunction with the VLBA and other HSA telescopes, subject to availability of matching observing systems (see below). Phased-VLA observing using two independently-tunable VLA sub-band pairs, one polarization pair (RCP+LCP) in the A0/C0 baseband pair, and the other (RCP+LCP) in the B0/D0 baseband pair, is available as a general capability. Any matching bandwidths available on the VLA as well as the VLBA DDC data system described above can be used. Bandwidths must be uniform at each station, across the entire VLBI array, and throughout the entire duration of the observation. In particular, VLA phasing and VLBI observing must be carried out at the same bandwidth. Bandwidths of 16 MHz and wider are available as a general capability. Bandwidths narrower than 16 MHz may work if the source is strong enough, but are expected to be of limited use. Y27 modes equivalent to the VLBA PFB and 8-channel DDC modes described above are also available on a shared risk basis, since they are less well tested. The restrictions are fewer for the VLA than for the VLBA or other stations, so the HSA guidelines should be followed. The VLA must be set up to match the VLBA; mixed modes are not allowed. Further details are available in the document VLBI at the VLA, and in the VLBA Observational Status Summary.

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

Semester 2015A proposals to use the GBT as part of the HSA will be considered. The GBT is equipped with the full VLBA Sensitivity Upgrade instrumentation, and is able to support all the observing configurations described in the VLBA Observing Capabilities section above. Further details may be found in section 4.7 of the GBT Proposer's Guide. Note that all proposals to use the GBT as part of VLBI must include time to set up the telescope (pointing, focus, etc.) prior to the start of the observation. This can take 0.5-1 hour depending on the frequency (see Chapter 6 of the GBT Proposer's Guide, and the GBT Observer's Guide, for further information).

The Effelsberg and Arecibo HSA stations have also installed the same wideband equipment as at the VLBA and GBT, but their implementation is not yet complete. An observing mode to match the PFB system works well for continuum science, but there is currently no mode to match the DDC for spectroscopy that has been fully commissioned. The following table summarizes the availability of the various observing systems for HSA stations for 2015A.

DDC-4 refers to a 4-channel, 2-IF mode, and DDC-8 to the full 8-channel, 4-IF case. The observing system must be identical for all stations in an observation. Combinations marked "RSRO" are only available through the Resident Shared Risk Observing program (below). Combinations marked "SRO" are available as "Shared Risk" observing, which means these are capabilities that have been verified to work with certain set-ups, but have not been extensively tested. Proposers should be aware that SRO and RSRO capabilities are generally not approved at priority A, owing to the level of risk associated with these observations.

Following a successful 3mm VLBI run between the Large Millimeter Telescope (LMT) in Mexico and the VLBA in May 2014, the LMT will be offered as a station of the HSA for 3mm observations with the VLBA for observing dates between 1 February 2015 and 31 May 2015, in semester 2015A.  The GBT may also be requested with the VLBA and LMT.  Access to VLBI using the LMT is provided through the VLBA RSRO program, and VLBA RSRO should be selected as the resource in the Proposal Submission Tool.  The LMT has a PFB-compatible, 2048-Mbps, recording system, and a dual polarization 3mm receiver with a tuning range exceeding that of the VLBA.  Proposers should use the VLBA capabilities to define their resource request when proposing to use the LMT for VLBI.

Global 3mm VLBI Array (GMVA)

VLBI proposals for observing at 3mm wavelength using the VLBA, GBT, Effelsberg, Pico Veleta, Plateau de Bure, Onsala, and Yebes telescopes should be submitted by 1 August 2014 through the NRAO Proposal Submission Tool. Successful proposals will be considered for scheduling in the May 2015 (or later) session. Proposers should be aware that at some GSTs the available time on the VLBA in the September 2015 session may be limited due to prior commitments (primarily in the Galactic Plane), and that the GBT may only observe at 3mm at night (i.e., 3 hours after sunset until sunrise; tests of daytime 3mm observing with the GBT are being undertaken for the GMVA, but should not be relied upon at this time). In order to maximize the sensitivity for continuum observations the GMVA will record at the highest bit rate the telescope instrumentation and resources permit. All telescopes will record at 2 Gbps; the only exception being Plateau de Bure, which will record in a compatible 1 Gbps mode.

For further details on proposing please consult the relevant administrative and technical information hosted at Bonn.

Proposal Preparation

Proposal preparation and submission for the VLBA, HSA, and GMVA are via the Proposal Submission Tool (PST) at NRAO Interactive Services. Use of the PST requires registration in the NRAO User Database.

Information about VLBA capabilities can be found in the VLBA Observational Status Summary. Questions may also be directed to the NRAO Helpdesk.