VLA Configuration Plans and Science Time Available

The February 1, 2021 deadline nominally covers the observing period September 22, 2021 through January 31, 2022 (Semester 2021B), encompassing the B configuration of the VLA. Multi-configuration proposals that include this configuration may also be submitted. Additionally, proposals requesting only configurations that will fall in semester 2022A (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.

The plot of estimated available observing hours as a function of LST for the B configuration in semester 2021B is shown below. In this plot, engineering, maintenance, and testing cause the solid (upper) line to be less than the total number of LST days in each configuration; such activities occur predominantly during daytime. Also subtracted from the total available science time estimate is the 648 hours allocated for the VLA Sky Survey (VLASS). 

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 from previous proposal deadlines, where green represents priority A, yellow priority B, and red priority C. For the net available time in this configuration per LST hour subtract the bars of the pre-committed time from the black curve.

We note that for the last few years the VLA has seen consistently lower demand for LSTs in the range of approximately 19 to 03 hours in almost all configurations. While we do not know for sure if this will be true for the B configuration in the 2021B observing semester, we encourage our users to submit proposals for time in that range. Furthermore, the above does not reflect the possible impact of a VLA extra-large proposal that is currently in its final review stage. If approved, about 193 hours of time will be allocated in the LST range 19 to 06 hours in the B configuration.

Observing Capabilities for Semester 2021B

For the 2021B 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.

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 has been updated and 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 54-86 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. The following capability is offered under the SRO program during the 2021B 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.

See the VLA Proposal Submission Guidelines web page 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. This access is provided in exchange for a period of residence to help commission those capabilities. Examples of capabilities that would fall under the RSRO program in the 2021B semester include:

• correlator dump times shorter than 50 msec, including integration times as short as 5 msec for transient detection;
• data rates above 100 MB/s;
• recirculation beyond a factor of 64 in the correlator;
• 4-band polarization or spectral line;
• 4-band coherent-dedispersion (YUPPI) pulsar observing;
• more than 3 subarrays, or subarrays with the 3-bit system;
• complex phased array observations (e.g., pulsar and complex VLBI observing modes);
• Frequency averaging by more than a factor of 4, or any frequency averaging in setups with mixed subband bandwidths, e.g., for spectral line+continuum with the averaging used in subbands designated for continuum;
• Rapid response capability: Automatically scheduling VLA observations in response to a trigger on shorter timescales than standard triggered proposals;
• eLWA: Joint LWA and VLA 4-band observations and correlations.

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 two commensal systems 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 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.

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 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, if not all, projects will be observed dynamically; users 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 also 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.