VLBA & HSA/EVN/Global Proposals

Since 2011, time on the VLBA and other NRAO instruments is scheduled on a semester basis, with each semester lasting six months.  Proposal deadlines are 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.   Time can be requested over multiple semesters if scientifically justified.

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.  Further instructions are available 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 approximately four weeks in advance of each semester submission deadline.  Currently, these deadlines are 5pm (1700) Eastern 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 NRAO Proposal Submission Tool (PST), available via NRAO Interactive Services.

   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.  A detailed description of the time allocation process is available.

   Approved programs are scheduled by the VLBA scheduling officers, who may be contacted at schedsoc@nrao.edu.  A "Guide to Using the VLBA" is available, aimed specifically at inexperienced users but also useful to fill in knowledge gaps for more experienced observers.

2. The High Sensitivity Array (HSA). The HSA comprises the VLBA in combination with the phased VLA, the GBT, Effelsberg, and/or Arecibo; observing time of up to 100 hours per trimester has been reserved for these observations.  Subsets of the HSA may also be requested.  All deadlines and procedures are the same as for the VLBA above.  Further information on "Observing with the High Sensitivity Array" is available in a separate document.
   
   The phased VLA rejoined the HSA as of observing semester 2013A, after a three-year gap during construction of the EVLA.  The functionality of the VLBA's RDBE unit is supported in the VLA by various elements dispersed throughout the system; phased-array output is written directly from the WIDAR correlator to a Mark 5C recorder.  An expanded (but still partial) set of modes will be available for semester 2015A.
   
   Arecibo only operates at frequencies up to 10 GHz, and can view sources only within 19.7° 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 provides access to the EVN User Guide.  Included in the guide is an EVN Status Table, giving details of current observing capabilities of all EVN stations; and the EVN Call for Proposals, which specifies EVN session dates and the wavelengths to be observed.  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.  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.  Such observations will be carried out during EVN sessions.
4. The Global Millimeter VLBI Array (GMVA).  This array consists of the eight VLBA stations outfitted with 3 mm receivers, together with Effelsberg, Pico Veleta, Plateau de Bure, Onsala, Metsähovi, and Yebes.  The European part of the GMVA is coordinated by the Max-Planck-Institut für Radioastronomie.  Observations are block-scheduled in two sessions per year.  More  details about the GMVA are available here.   GMVA proposals are submitted twice per year at the 1 August and 1 February NRAO deadlines, and beginning for the 2014A semester, GMVA proposals are only submitted through the NRAO PST, via NRAO Interactive Services, as for the VLBA and HSA.
   

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 in the "Guide to Using the VLBA".