Introduction

by Gustaaf Van Moorsel last modified Mar 10, 2017 by Lorant Sjouwerman

Abstract

This document describes the web-based tool to create Scheduling Blocks (SBs): machine readable instructions for radio astronomical observations using the Karl G. Jansky Very Large Array (VLA) and its WIDAR correlator.

This Observation Preparation Tool web application (OPT web application) consists of three separate tools that are used in conjunction. These are the Source Catalog Tool (SCT) to define and select positions in the sky, the instrument Resource Catalog Tool (RCT) to define and select hardware (receiver and correlator) settings, and the Observation Preparation Tool (OPT) to define and create a sequence of scans where a scan is a combination of an observing mode, a source, a resource, a time interval, and a scan intent.

This manual guides the reader through the three tools, providing adequate information and scheduling hints to create an observing schedule for observations with the VLA and how to submit the schedule to VLA operations. Considerable observing details and suggestions are collected in the VLA Guide To Observing. Additional specific guidance can be obtained through the NRAO Helpdesk.

The VLA will be observing in a mode where the observing schedule to be executed is selected from a pool of valid schedules just before the actual observations take place. This Dynamic scheduling is described in the VLA Guide To Observing. The life-cycle of the SB, some practical considerations for a higher success rate in the observing pool and, e.g., more detailed instructions for performing line observations that depend on Doppler calculations can be found there.

The Observation Preparation Tool web application (OPT) is a product of the National Radio Astronomy Observatory staff. The Karl G. Jansky Very Large Array (VLA) is operated by the National Radio Astronomy Observatory (NRAO), which is a facility of the National Science Foundation (NSF) operated under cooperative agreement by Associated Universities, Inc. (AUI).

 

Purpose of this Document

The purpose of this document is to provide help to the individual preparing VLA observations with the WIDAR correlator. This document consists of an introduction to the Observation Preparation Tool (OPT) web application, hints and preliminary "cookbook"-like approaches to create a successful observing schedule. This document is not suited to learn, nor intended to teach, observing strategies and good observing practices. The Observational Status SummaryVLA Guide To Observing, and other VLA documentation are great resources with further references. For more specific questions one may consult the NRAO Helpdesk.

An observing schedule using the VLA receivers, electronics and correlator is made through the OPT web application. It consists of a description of an observing run: a Scheduling Block (SB) that is made up of a sequence of observing scans. To make full use of the OPT, it may be necessary to predefine (enter) sources to be observed using the Source Catalog Tool ( SCT), and to possibly predefine the frequency and correlator settings to be used using the hardware and instrument configuration Resource Catalog Tool (RCT). This document should aid in creating source and resource lists, and creating the final observing schedule (an SB). Alternatively, if no user catalogs are defined, one can resort to observing known (calibrator) sources using standard correlator settings, although using these catalogs only may be rather restrictive in scientific discovery space.

 

Abbreviations Used in this Document

The OPT, SCT and RCT abbreviations were introduced in the previous section.  When referring to the OPT in the remainder of this document, it is implicitly referring to the tool that creates a sequence of observing scans. On the other hand, when we refer to the OPT web application we specifically refer to the combination of tools consisting of OPT, SCT, and RCT.

The use of the term '(re)source' is short-hand for the text "source and resource": the sentence applies to both source and resource. Similarly, using 'project (etc.)' allows us to avoid having to write "project, program block(s), scheduling block(s), and scan(s)" which otherwise would make sentences confusing. For program block and scheduling block we will use PB and SB, respectively, or blocks when we mean either or both.

We will further use PST (Proposal Submission Tool) and TAC (Time Allocation Committee), which have some interaction or influence on what goes on in the OPT web application.