VLA Configuration Plans and Science Time Available

The July 31, 2024 proposal deadline covers the observing period February 21, 2025 through August 25, 2025 (Semester 2025A), corresponding to the D and C configurations of the VLA. Multi-configuration proposals that include this configuration may also be submitted. Additionally, proposals requesting only configurations that will fall in semester 2025B (or later) may be submitted if the Principal Investigator is a graduate student. NRAO offers this service to provide scientific and technical feedback for students, and to provide them with an opportunity to re-submit their proposals for their principal semester with this information in hand. Students should ensure that their status is up to date and correct in the NRAO User Database. Please refer to the VLA Configuration Plans for details and availability of upcoming configurations.

Plots of estimated available observing hours as a function of LST for the D and C configurations in semester 2025A are shown below. In these plots, engineering, maintenance, and testing cause the solid (upper) line to be less than the total number of LST days in this configuration; such activities occur predominantly during daytime.

Estimated science time available per LST hour is shown by the solid (upper) black line for all frequencies, the dashed (middle) line for K-band conditions, and dotted (lower) line for Q-band conditions. The colored bars show pre-committed time where green represents priority A, yellow priority B, and red priority C. The lighter green, yellow, and red represent high frequency (HF; K through Q bands) priority A, B, and C, respectively. For the net available time in this configuration per LST hour subtract the bars of the pre-committed time from the black curve. The pre-committed time in this plot consists of A-priority not completed in previous configurations and proposals from previous semesters that requested future configurations.

In total, we expect 2910 hours to be available for open skies observing in the 2025A semester; 1461 hours in the D configuration and 1449 hours in the C configuration.

VLA Proposal Types 

In addition to Regular Proposals, Large proposals (those which request 200 hours or more) are particularly encouraged and welcome on the VLA. Such proposals should follow the instructions for Large proposals in the NRAO & GBO Users' Policy. Large proposals which require multi-semester observations are often supported. Filler proposals are also encouraged – these are scientifically useful programs, preferably utilizing the lower frequency bands of the VLA, that can be scheduled over a large range of LST using short (2 hours or less) scheduling blocks. Such projects can help to fill gaps in the dynamic observing schedule. Programs requesting time at lower frequencies (C-, S-, and L-bands) are particularly encouraged.

Filler proposals can be submitted as Regular proposals or Large proposals (the Users' Policy instructions for Large proposals still apply); either Large or Regular filler proposals can be multi-semester proposals if scientifically justified. Filler proposals should be explicitly identified as such and will normally only be considered for filler time (i.e., priority C) regardless of their ranking. See the instructions for Filler Programs in the NRAO & GBO Users' Policy for further information.

Observing Capabilities for Semester 2025A

For the 2025A semester the General Observing (GO) capabilities are given in the Offered VLA Capabilities during the Next Semester section of the Observational Status Summary (OSS) and are summarized in the following table. Several additional capabilities are available to proposers through the Shared Risk Observing (SRO) and Resident Shared Risk Observing (RSRO) programs, as described below.

Important Update: Starting with the 24B Call for Proposals, the VLA General Observing Setup Tool (GOST) has been made obsolete. The NRAO requires the use of a proposing-specific version of the Resource Catalog Tool (RCT) for proposers requesting spectral-line or non-default VLA WIDAR resources. For more details and to access the new proposal specific version of the tool, please visit https://go.nrao.edu/pst-rct.

Both single pointing and mosaics with discrete, multiple field centers are supported. Data rates up to 60 MB/s (216 GB/hour) are considered GO. Correlator integration time limits per band and per array configuration also apply as described in the OSS. The data rate and total data volume required by a proposal will be a consideration in its technical evaluation.

There are some limitations on frequency settings and tuning ranges, especially at Ka-band; please consult the OSS for further details. Additionally, the Exposure Calculator is available to estimate sensitivities, while other special tools are available to assist users with the development of correlator setups for the proposal deadline (see VLA Proposal Submission Guidelines). All antennas employ electronics and receiver systems that provide continuous frequency coverage from 1–50 GHz in the following observing bands: 1–2 GHz (L-band); 2–4 GHz (S-band); 4–8 GHz (C-band); 8–12 GHz (X-band); 12–18 GHz (Ku-band); 18–26.5 GHz (K-band); 26.5–40 GHz (Ka-band); and 40–50 GHz (Q-band). In addition to these, all VLA antennas are equipped with 200-500 MHz (P-band) and 54-84 MHz (4-band) receivers near the prime focus.

We continue to offer shared risk programs to our user community for those who would like to push the capabilities of the VLA beyond those offered for general use.

VLA Shared Risk Observing

The VLA Shared Risk Observing (SRO) program allows users access to capabilities that can be set up via the Observation Preparation Tool (OPT) and run through the dynamic scheduler without intervention, but are not as well tested as GO capabilities. Data rates higher than 60 MB/s (216 GB/hour) and up to 100 MB/s (360 GB/hour) are considered SRO. In addition, the following capabilities are offered under the SRO program during this semester:

• On-the-Fly (OTF) mosaicing for X-, Ku-, K-, Ka-, and Q-bands (used when each pointing on the sky is no more than a few seconds), but not using subarrays.
• Wideband VLA for VLBI: Enables recording of VLA WIDAR continuum-mode correlations during VLA phased array (Y27) VLBI observations. Currently, this only supports standard VLA 8-bit continuum modes with a 2-GHz bandwidth. See the VLBA Call for Proposals for more details.
• eLWA: Joint LWA and VLA 4-band observations using a single 8 MHz subband centered at 76 MHz, and 4-bit VDIF output.
  Note: During semester 2025A, the LWA is expected to be undergoing infrastructure upgrades and availability of the telescopes (LWA1 and LWA-SV) may be limited.  Those interested in using this mode should contact Greg Taylor at gbtaylor@unm.edu for more details.

Proposers should be aware that SRO projects will not be carried over to future semesters if they cannot be scheduled for reasons associated with the shared risk component(s) of the observations, even if awarded scheduling priority A.

See the VLA Proposal Submission Guidelines for information about tools and other advice on proposing for Shared Risk observing capabilities.

VLA Resident Shared Risk Observing

The VLA Resident Shared Risk Observing (RSRO) program provides access to extended capabilities of the VLA that require additional testing and might require lower-level access to the software system (hand-crafted observing scripts, for instance). This access is provided in exchange for a period of residence to help commission those capabilities. Users are encouraged to conceive and propose innovative ideas for new VLA capabilities. Some staff suggestions can be found at the VLA RSRO program section of the VLA OSS.

Proposers should be aware that RSRO projects are generally not approved at scheduling priority A, owing to the level of risk associated with these observations. Also, RSRO proposals will not be carried over to future semesters if they cannot be scheduled, similar to SRO proposals.

A detailed description of the VLA RSRO program is available at the VLA Proposal Submission Guidelines web page.

Commensal Observing Systems at the VLA

There are currently three commensal systems in operation on the VLA that may take data at the same time as your proposed observation. The first is the VLITE system, which will take data at P-band during regular observations that use bands other than P-band. Hence, VLITE is turned off by default during P-band or dual 4/P-band observations. The VLITE system is deployed on up to eighteen VLA antennas. Observers wishing to gain access to the commensal VLITE data taken during their VLA observations should follow the instructions on the VLITE web page for doing so. The collection of VLITE data during observation can be disabled in the OPT if desired.  The second is the realfast system, which takes data at very fast dump rates in an effort to detect Fast Radio Bursts (FRBs). This system is fully commissioned for observing at L- through X-bands, in parallel with standard continuum correlator configurations. The collection of realfast data can similarly be disabled if desired, by selecting a resource that is not enabled for realfast observing.  The third is COSMIC SETI, which enables the search for extraterrestrial intelligence (SETI) using the VLA, and collects data during unconflicted PI science observations. Similar to VLITE, collection of COSMIC SETI data can be disabled in the OPT when setting up observations.  For information about commensal observing see the Commensal Observing with NRAO Telescopes page.

Proposal and Observation Preparation

Proposal preparation and submission are via the Proposal Submission Tool (PST) at NRAO Interactive Services. Use of the PST requires registration in the NRAO User Database. There are various tools and documentation to help users in this process. Descriptions of all updated documentation and tools, along with an outline of the steps required to write a proposal, are available at the Guide to Proposing for the VLA web page.

When constructing sessions in the PST, proposers should be cognizant of their use by the Telescope Time Allocation Committee (TAC). Specifically taking into account the time available as a function of LST, software will assign an initial scheduling priority to each session in each proposal, which can be modified by the TAC if they desire. The assigned scheduling priority will depend on the linear-rank score of the proposal from its scientific review, the LSTs involved in the session (daytime is harder to accommodate than nighttime, for instance), the predicted atmospheric conditions for observing over that LST range at the time of year of the configuration, the total time requested in the session, and the competition from other proposals requesting time at similar LSTs. Please see this description for guidance on how to set up sessions in the PST, and this document for a complete description of the VLA Prioritizer (the software that generates the initial scheduling priorities for all sessions that are subsequently used by the TAC to derive the final priorities).

All approved VLA observations are set up using the Observation Preparation Tool (OPT). Most projects will be observed dynamically; users granted dynamic, non-triggered time, must either submit their scheduling blocks before the start of the configuration or contact the VLA Scheduler (schedsoc@nrao.edu) before that date to avoid a reduction in scheduling priority. Early submission maximizes the opportunity of them being observed and helps us to schedule the VLA most efficiently. Advice on the optimal length of scheduling blocks and other useful information may be found at the Observing FAQ web page.

Information about VLA capabilities, proposal preparation and submission, observing strategies, and calibration overhead can be found in the VLA Observational Status Summary, at the Guide to Proposing for the VLA, and at the Guide to Observing with the VLA. Answers to Frequently Asked Questions are contained in these proposing and observing guides. Questions may also be directed to the NRAO Helpdesk.