17.1 Proposal Preparation and Submission

Starting in 2011 time on the VLBA will be scheduled on a semester basis, with each semester lasting six months. Proposal deadlines will be February 1 and August 1, with the February 1 proposal deadline nominally covering time to be scheduled during the following August through January, and the August 1 deadline covering time to be scheduled from February through July.

Observing proposals may specify the VLBA, or the VLBA in combination with various other VLBI arrays. It should be noted, however, that proposals to use the European VLBI Network (EVN) and Global cm VLBI are handled by the EVN on a trimester system, with proposal submission deadlines of February 1, June 1, and October 1. Please see http://www.nrao.edu/admin/do/vlba-gvlbi.shtml for further instructions on proposal preparation and submission for the various types of VLBI arrays.

1. The VLBA alone. A Call for Proposals is published in the NRAO eNews at http://science.nrao.edu/enews/ approximately two weeks in advance of each semester submission deadline. Currently, these deadlines are 5pm (1700) Easter Time on February 1, and August 1 (if the deadline falls on a holiday or weekend, it is extended to the next working day). VLBA proposals must be prepared and submitted using the Proposal Submission Tool (PST), available at http://science.nrao.edu/vlba/obsprop/pst.shtml.

   All proposals will be reviewed by a Science Review Panel (SRP) in relevant subdisciplines (e.g., solar system, stellar, galactic, extragalactic, etc.). The SRP's comments and rating are strongly advisory to the NRAO Time Allocation Committee (TAC), and the comments of both groups are passed on to the proposers soon after each meeting of the TAC (twice yearly) and prior to the next proposal submission deadline. See http://science.nrao.edu/observing/peta.shtml for a detailed description of the time allocation process.

   Approved programs are scheduled by the VLBA scheduling officers, who may be contacted at ``schedsoc@nrao.edu''. Ulvestad (2004) provides a short guide to using the VLBA, aimed specifically at inexperienced users but also useful to fill in knowledge gaps for more experienced users.

2. The High Sensitivity Array (HSA). The HSA comprises the VLBA in combination with the VLA², the GBT, Effelsberg, and/or Arecibo Observing time of up to 100 hours per trimester has been reserved for these observations; this opportunity, including the specification of the HSA in the proposal, is described at http://science.nrao.edu/vlba/obsprop/HSA.shtml . Stations from this set also may be requested individually as a subset of the High Sensitivity Array. All deadlines and procedures are the same as for the VLBA above.

   Users should be aware that Arecibo only operates at frequencies up to 10 GHz, and can view sources only within $19.7^\circ$ of its zenith; see http://www.naic.edu for further information about Arecibo's properties.

3. The European VLBI Network (EVN) and Global cm VLBI. The EVN consists of a VLBI network of stations operated by an international consortium of institutes (Schilizzi 1995). The EVN home page at http://www.evlbi.org provides access to the EVN User Guide. That guide includes the EVN Status Table, giving details of current observing capabilities of all EVN stations; and the EVN Call for Proposals, describing how to apply for observing time on the EVN. The EVN provides proposal, review, and scheduling mechanisms for such programs, and conducts regular sessions of 2-3 weeks, 3 times per year, to carry out these observations. EVN proposal deadlines are February 1, June 1, and October 1, with no allowance made for weekends. EVN session dates, and the wavelengths to be observed, are given in EVN Calls for Proposals at http://www.ira.inaf.it/evn_doc/call.txt. Proposals requesting the EVN in combination with the VLBA or other affiliates are classified as ``Global cm VLBI''. EVN and Global cm VLBI proposals must be prepared and submitted to the EVN using the EVN's NorthStar Tool, available at http://proposal.jive.nl/. Such observations will be carried out during EVN sessions.

4. The Global 3 mm Array. This array consists of the VLBA stations outfitted with 3 mm receivers, together with Effelsberg, Pico Veleta, Plateau de Bure, Onsala, and Metsähovi. The European part of the 3 mm Array is coordinated by the Max-Planck-Institut für Radioastronomie. For more details and to submit a proposal, see http://www.mpifr-bonn.mpg.de/div/vlbi/globalmm/ .

The NRAO SCHED program (Walker 2011) can be used to determine the Greenwich Sidereal Time range during which the VLBI target sources are visible at various stations. This program can also be used to evaluate the $u$-$v$ plane coverage and synthesized beams provided by the selected array.

A source position service is available through NRAO to obtain accurate positions for use in correlation (Walker 1999a). This should be requested simultaneously with the proposal, if not earlier. Requirements for source position accuracy in correlation are discussed by Ulvestad (2004).