VLA Configuration Plans and Science Time Available

The 3 August 2015 deadline covers the observing period 5 February 2016 through 3 October 2016 (Semester 2016A), corresponding to the C, CnB, and B configurations. Multi-configuration proposals that include C, CnB, or B configurations may also be submitted. In addition, proposals requesting only configurations that will fall in semester 2016B 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.

Note that semester 2016A is the last semester NRAO will offer any hybrid configuration, and only the CnB hybrid may be requested. Proposers with questions about how this may impact their proposal should contact the NRAO Helpdesk as soon as possible.

Plots of estimated available observing hours as a function of LST and weather conditions for all configurations in semester 2016A are below. In these plots, engineering, maintenance, and testing cause the solid (upper) line to be less than the total number of LST days in the configuration; such activities occur predominantly during daytime.

The length of the B configuration noted above has been extended to accommodate the possible start of observing for the VLA Sky Survey. If the Sky Survey does not proceed in semester 2016A, then the B configuration will revert to its normal length. The number of hours available for PI science in the upcoming B configuration is approximately the same in either case.

(click image to enlarge)
C-configuration	CnB configuration	B-configuration
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 time already committed in previous proposal rounds, where green represents priority A, yellow priority B, and red priority C. For the net available time in 2016A per LST hour subtract the bars of the pre-committed time from the black curves.

Observing Capabilities for Semester 2016A

The capabilities offered for 2016A through our General Observing (GO) program are the same as those offered for 2015B; details are given in the VLA 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 will be supported. Data rates up to 25 MB/s (90 GB/hour) will be available to all users and, with additional justification, data rates up to 60 MB/s (216 GB/hour) will be available. 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 set-ups for the proposal deadline (see VLA Proposal Preparation and Submission). 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).

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 well tested. The following capabilities are offered under the SRO program in Semester 2016A:

• On-the-Fly (OTF) mosaicing (used when each pointing on the sky is no more than a few seconds)
• 32 sub-bands per baseband with the 8-bit samplers
• recirculation of up to a factor of 64
• 8-stream recording with phased VLA for VLBA observing.

See the VLA Proposal Preparation and Submission 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, in exchange for a period of residence to help commission those capabilities. Examples of capabilities that would fall under the RSRO program in Semester 2016A include:

• correlator dump times shorter than 50 msec, including integration times as short as 5 msec for transient detection;
• pulsar observations;
• data rates above 60 MB/s;
• recirculation beyond a factor of 64 in the correlator;
• P-band system (230 to 470 MHz) polarimetry and spectroscopy;
• 4-band system (54 to 86 MHz; see Low Frequency Observing section below);
• more than 3 sub-arrays, or sub-arrays with the 3-bit system;
• complex phased array observations (e.g., pulsar and complex VLBI observing modes); and
• frequency averaging in the correlator: a new capability for averaging to wider frequency channels in the correlator has been developed that will reduce the data volume for all continuum subbands

A detailed description of the VLA RSRO program for semester 2016A and beyond is available at the VLA Proposal Preparation and Submission web page.

Low Frequency Observing

The new low frequency receiver system developed in collaboration with the Naval Research Laboratory will be available for Stokes I continuum observations at P-band (230 to 470 MHz) through the GO program. Use of the P-band system for polarimetry and/or spectroscopy will be through the RSRO Program. The new receivers also work at 4-band (54 to 86 MHz), and new feeds have been deployed on six VLA antennas. Observations at 4-band are also available through the RSRO program.

Finally, the commensal VLITE system will take data at P-band during regular observations that use bands other than P-band.  The VLITE system is deployed on ten 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.

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 VLA Proposal Preparation and Submission web page.

When constructing sessions in the PST, proposers should be cognizant of their use by the Time Allocation Committee (TAC). Specifically, taking into account the time available as a function of LST, the TAC will assign a scheduling priority to each session in each proposal. The assigned scheduling priority will depend on the linear-rank score of the proposal, the LSTs involved in the session (daytime is harder to accommodate than nighttime), the total time requested in the session, and the competition from better-ranked proposals requesting time at similar LSTs. Please see the description of the VLA prioritizer for further details.

All approved VLA observations are set up using the Observation Preparation Tool (OPT). Most, if not all, projects will be observed dynamically; users should submit scheduling blocks early in the configuration to maximize the opportunity of them being observed. 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, observing strategies, and calibration overhead can be found in the VLA Observational Status Summary, at the Guide to Observing with the VLA, and at the Observing FAQ web page. Questions may also be directed to the NRAO Helpdesk.