1. Develop rationale: Before writing a proposal, the proposer must develop the scientific rationale for the program, develop a source list, decide on the observing band(s) to be used, and estimate the expected source strengths and their detectability. For spectral-line sources, the proposer also must decide on the desired velocity resolution, and convert that to a spectral resolution.
2. Complete coversheet: A proposal consists of a 2-page cover sheet and a scientific justification containing 1000 words or fewer, plus any accompanying figures. Instructions and a standard LaTeX template are available here.

   Various types of Rapid Response science can be proposed as well, some outside the normal deadlines.

   The most confusing entries on the cover sheet are items 9, 11 and 13 through 18. Some reasonable defaults are discussed below:

• (9) Recording format: You may check a single box for the VLBA continuum defaults. For spectral lines, choices of modes will depend on the desired velocity resolution. Some generally good choices for line observations are to use 2-bit samples, choose the number of BBC channels and their widths based on the expected frequency coverage of the lines, leaving some continuum on either side available for calibration, and use Nyquist sampling (two samples per hertz of bandwidth) except in the case of oversampling on very narrow bandwidths. For example, if one is observing two lines that are separated by 16 MHz and are each 4 MHz wide, one might use 4 BB channels (two at each polarization) of 16 MSamples/sec (corresponding to 8 MHz bandwidth each) with 2-bit sampling. Then, the baseband frequencies would be adjusted to center the lines in the two right/left polarization pairs.
• (11) Telescope request: Most observations request only the VLBA. However, for observations that need considerably more sensitivity, it also is possible to request larger telescopes. Proposers wishing the best sensitivity may consider proposing for the High Sensitivity Array, including the VLA, Green Bank Telescope, Arecibo and Effelsberg. For observations that need more short spacings, a single VLA antenna may be requested. Finally, for programs that require more sensitivity, more short baselines, or transatlantic baselines, proposers also may ask for antennas from the European VLBI Network (EVN). All proposals that request telescopes in addition to the 10 VLBA antennas must include a specific rationale for those telescopes in the scientific justification.
• (13) Observation type: This is usually interferometry. If the source is weaker than 50-100 mJy at centimeter wavelengths, phase referencing must be used and also should be checked. It then is useful to identify the phase-reference source and its suitability in the body of the proposal.
• (14) Dynamic scheduling: This refers to scheduling that takes best advantage of required weather and telescope conditions to optimize all the science done on the VLBA. Proposals are not suitable for dynamic scheduling if they require coordination with external observatories (including the VLA and GBT) and/or specific (rather than approximate) intervals between multiple epochs.
• (15) Polarization: Dual Circular Polarization is usually best for spectral-line observations, to increase the signal-to-noise in a limited bandwidth.
• (16) Tape usage: The recording time and total time need not be entered unless they are substantially different. The maximum sustainable data rate for the VLBA is currently 128 Mbit s^-1, and may be exceeded only for proposals with very strong scientific justifications. However, it often is possible (for example) to observe at 256 Mbit s^-1 with the recording time set to half the total time allocation. This is useful because it may enable a shorter phase-referencing cycle and better atmospheric calibration.

• (17) Assistance required: Proposers are welcome to ask for extensive help in order to make sure that they get the details right. For VLBA-only data, users may request data calibration by NRAO.
• (18) Processor: For VLBA-only observations, this is almost certainly the Socorro correlator. Other correlators might be used for global observations, 86-GHz (3-mm) observations, and/or some specialized astrometric observations. All the "special processing" options may be left blank if standard continuum observations are desired. For line observations, the averaging time and number of spectral channels per baseband channel should be determined based on the spectral resolution desired, and the field of view to be imaged. The VLBA Observational Status Summary gives formulae for how wide a field can be imaged as a function of correlaor integration time and spectral resolution. There are limitations on the number of spectral channels (due to finite number of FFT processors) and on the product of baselines and spectral channels divided by integration time (due to the upper limit on the correlator output rate). See Correlator Capabilities for details.
3. Submit: The preferred submission method is to send the postscript file of the proposal by email to propsoc@nrao.edu. Paper submissions are also accepted.

Introduction Why use the VLBA? How to propose Proposal selection: refereeing and observing allocation Schedule preparation Observations, correlation, data validation, and distribution Calibration Final imaging and analysis Staff collaboration, financial support for data reduction, scientific results and publications, graduate student programs

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