VLBA, HSA, and GMVA Proposal Guide

Proposal submission information for the following three combinations of telescopes are detailed in individual sections below:

 

VLBA Proposals

The VLBA provides ultra-high angular resolution for astrophysical studies including:

  • Non-thermal continuum emission, including polarimetry, from active galactic nuclei (AGN), Galactic micro-quasars, pulsars, and other sources.
  • Maser emission lines of OH (1.7 and 6.0 GHz), CH3OH (6.7 and 12.2 GHz), H2O (22 GHz), SiO (43 and 86 GHz) and other molecules, and numerous thermal absorption lines, in a variety of Galactic and extragalactic circumstances.
  • Multiple-phase-center surveys across the primary beam.
  • Parallax and proper motion via differential astrometry of a variety of stars, star-forming regions, and nearby extragalactic objects, at accuracies as good as 10 microarcsec.
  • Absolute astrometry at accuracies of ~200 microarcsec to expand the International Celestial Reference Frame.

Overall information about the VLBA is available in the VLBA Observational Status Summary (OSS); specific sections relevant to various proposal types are linked below.

The VLBA operates two data systems, a Polyphase Filterbank (PFB), and a Digital Downconverter (DDC). These are described in detail in the Roach Digital Backend (RDBE) section of the VLBA OSS, which also includes suggestions for selecting the optimal observing system for various scientific goals.

VLBA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services.  Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database.

Proposals requiring significant additional correlator resources, such as multiple phase centers per field or multiple pulsar phase bins, should consider mechanisms to support the correlation without adversely affecting the throughput of other projects.  These should be entered in the technical justification section of the proposal.

Approximately 1000 to 1200 hours of VLBA observing time are expected to be available for Open Skies in observing semester 2020B.  In recent semesters, there has been less pressure in the GST range 0600 - 1800 hours as compared to 1800 - 0600 GST, and we expect this trend to continue.

Most approved VLBA observations are performed dynamically; for those dynamic observations, users must either submit their observing (.key) files (to vlbiobs@nrao.edu) before the beginning of the semester (February 01 or August 01 for A and B semesters, respectively), or contact the VLBA Scheduler (schedsoc@nrao.edu) before those dates to avoid a reduction in scheduling priority. Early submission of schedules maximizes the opportunity of dynamic observing and assists in the efficient scheduling of the VLBA.

NRAO Staff Assistance with VLBA Observation Setup and Data Reduction

Beginning with the 2020A proposal call, NRAO offered extra staff assistance with VLBA observational setups and data reduction.  We will continue to offer this assistance for the 20B semester.  Again, this offer will pertain to proposals which request only the VLBA (i.e. no HSA, GMVA, or cm Global proposals).   Additionally, this offer will be limited in scope to new or novice VLBA users, and will include both observing and data reduction assistance.   There will also be limitations in some capabilities which will be supported under this program, for example which bands will be allowed.  In order to request this assistance, please mark the checkbox on the General page of VLBA proposals in the Proposal Submission Tool (PST), at the bottom of the page, and please provide input on your proficiency, and/or specific requests in the text box.   Note  that checking the text box and providing the requested input does not automatically mean that this service will be provided for your proposal.  There will be an internal NRAO review of these requests similar to that done for RSRO proposals (see below); the proposal disposition letter will inform the proposers whether or not the service can be provided.

VLBA Filler Proposals

Filler proposals, which are scientifically useful programs which can be scheduled at a large range of GST times, with fewer than 8 stations, low-frequency weather requirements, and short (2 - 6 hours) scheduling blocks, are especially encouraged on the VLBA.  Such  projects can help to fill "gaps" in the dynamic observing schedule

VLBA Resident Shared Risk Observing

The VLBA Resident Shared Risk Observing (RSRO) program provides users with early access to new capabilities in exchange for a period of residency in Socorro to help commission those capabilities. For example, the phased-VLA system was developed through RSRO programs.  Users are encouraged to conceive and propose innovative ideas for new VLBA capabilities. Some staff suggestions are at VLBA RSRO program, along with details for submitting RSRO proposals.  

Proposers should be aware that RSRO capabilities are generally not approved at priority A, owing to the level of risk associated with these observations.

 

High Sensitivity Array (HSA) Proposals

The HSA comprises the VLBA, phased VLA, GBT, Effelsberg, and Arecibo telescopes. All of the HSA stations are equipped with instrumentation compatible with the VLBA observing capabilities described in Roach Digital Backend (RDBE) section of the VLBA OSS.  Ongoing special considerations for the HSA telescopes are documented in the HSA section of the VLBA OSS; new features and special cases are cited here.

VLBI observations combining the VLBA with any one or more of the other four HSA stations can be requested in a single HSA proposal.  However, separate proposals must be submitted for any non-VLBI use of any requested telescopes.

HSA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services.  Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database.  The inclusion of HSA stations should be quantitatively justified in the proposal.

4096 Mbps on the HSA (SRO)

The highest recording rate on the VLBA (4096 Mbps) can be requested for the HSA, as a shared-risk observing (SRO) mode, for semester 2020B.  This includes the VLBA itself, Effelsberg, the phased VLA (Y27) and the GBT, but excludes Arecibo (see below).  The EVN Sensitivity Calculator can select 4096 Mbps for sensitivity estimates on the HSA.

HSA Station Notes

• The phased Very Large Array (Y27) will be available for HSA observing in Semester 2020B, in the B (~Aug - Sep 2020) and A (~Oct 2020 - Jan 2021) configurations.  Please note that high frequencies (at receiver bands 22 GHz and above) have better phasing in the more compact configurations (C and D).  High frequency phasing in the extended configurations in the summer can be quite difficult.

• Due to varied pressures on the Green Bank Telescope's (Gb) scheduling resulting from the transition to reduced open skies time by the NSF, HSA observations will likely have to be ranked at least in or near the top 10-15% of all AUI telescope proposals in order to be accepted.  Proposers should clearly justify the need for the GBT in the text of the proposal.  All proposers requesting the GBT should include any needed setup and overhead time in the total time request for their proposals. Additionally, proposers should be aware that long scheduling blocks (more than 6 hours) will be difficult to schedule owing to constraints coming from non-open skies time.  Proposers are encouraged to make clear in the technical justification section any constraints about how observing time could be broken into smaller pieces without adversely affecting the proposed science; include information as relevant regarding maximum elapsed time of a split schedule and minimum scheduling block lengths.

Observations using the GBT 6-cm receiver as part of the HSA must be taken, correlated, and calibrated in full Stokes mode.  Due to the large cross-talk between polarizations, only total intensity (Stokes I) data will be usable. 

• The Effelsberg (Eb) 100-m telescope supports both the PFB and DDC observing systems available on the VLBA.  Consult this web page for more detailed information about the Eb HSA station.

• The Arecibo (Ar) 305-m telescope is continuing its upgrade of the observing system to include the DDC mode of the RDBE digital backend.  Mark 6 recording, the DDC mode (as well as PFB), and 4096 Mbps data rates all are expected to be available at Ar for the 2020B semester, but since all these components have not been widely tested, a proposer must use the RSRO Observing Mode in the PST to select these for Ar.  For questions about the use of Arecibo in the HSA while writing proposals, please use the NRAO helpdesk.   

The sensitivity of VLBI observations with Ar changed after the 2017 hurricanes at the station, due to flooding which altered the shape of a portion of the main reflector.  Please use the EVN Sensitivity Calculator for the most up-to-date values.

The latest information about VLBI observing at Arecibo can be found at the AO VLBI website.

 

Global 3mm VLBI Array (GMVA) Proposals, including Phased ALMA

GMVA proposals submitted by the 2020 February 3 deadline will be considered for scheduling in 2020 Session II  (Oct 08 - Oct 13), or later sessions.

Complete information on the GMVA is available at the GMVA website.  Ongoing special considerations are documented in GMVA section of the VLBA OSS; new features and/or special cases are cited here.

As noted in the HSA section above, GBT time available for VLBI has been reduced due to its new partnership arrangements.

GMVA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services.  Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database.  The inclusion of the GBT and/or ALMA in a GMVA proposal should be quantitatively justified.  ALMA and/or the KVN must be specified by entering "ALMA" or "KVN" as "Other" entries in the PST.

The GMVA will record at the highest bitrate which instrumentation and resources permit. Currently all telescopes will record at 4096 Mbps (except the KVN, which will record in a 1024 Mbps mode).

Note that the availability of NOEMA (Plateau de Bure) for GMVA Session II in 2020 and later sessions is not confirmed.

Another opportunity to propose VLBI observations using the phased ALMA telescope will be available at this Call for GMVA proposals:

It is expected that phased ALMA will participate in some GMVA observations during ALMA Cycle 8 (Oct 2020 - Sept 2021;  see the ALMA Cycle 8 Pre-announcement).   There are likely to be ~43 ALMA antennas available for GMVA observations; but the phased sum used for VLBI may be constructed only from those that lie within a circle of radius 0.5 km.   GMVA session dates for 2021 are not yet fixed but Session I in 2021, which is traditionally in the period March - May, would provide an opportunity for  GMVA + ALMA observing. 

Any GMVA proposal requesting phased ALMA during Cycle 8 must be submitted via the NRAO PST at the February 3, 2020 deadline.

Proposers should:

  • specify "ALMA" in the Other Stations text field in the PST
  • select the default GMVA 3mm observing mode of 4096 Mbps, dual polarization
  • specify the amount of time and GST range(s) needed for ALMA separately, either in Session Constraints or Comments, or in the Technical Justification.

A separate proposal to ALMA must also be submitted at the deadline for ALMA Cycle 8 proposals on April 21, 2020.  For this, all proposers (PI and Co-I's) must be registered ALMA users (see:  http://www.almascience.org).

Restrictions on GMVA+ALMA proposal in Cycle 8:

  • GMVA observations with ALMA will be limited to a fixed recording mode, which currently provides 4096 Mbps on all baselines.  The KVN will not be available in this mode.  Only VLBA telescopes will be available at 7mm in this mode.
  • Direct phasing of the ALMA array is limited to targets with a correlated flux density >0.5 Jy contained within an unresolved core on ALMA baselines up to 1 km.  Direct phasing on the science target ("active" phasing) thus puts a lower limit on the brightness of the science target.
  • For weaker sources, the option of "passive" phasing will be introduced in Cycle 8.  In this mode, the ALMA array is periodically phased on a bright calibrator close in angular distance to the science target.  (This mode has been in use for VLBI at the VLA for many years.)  There are thus no restrictions on the flux density of science targets using passive phasing (aside from SNR considerations on VLBI baselines).  The properties of the phasing calibrator must meet the same criteria as for actively phased observations, and it is recommended that the phasing calibrator lie within an angular separation of no more than 5 degrees from the science target.  Proposers must specify the phasing calibrator in their proposal; consult the ALMA calibrator catalog.
  • In order to make a clean linear-to-circular polarization transformation of ALMA recordings, any target source must be observed for a duration of at least 3 hours (breaks for calibrators permitted) to sample a range of parallactic angles.
  • Large Programs (>50 hours of observing time) are not permitted because phased ALMA is a non-standard mode.
  • No long-term programs may be proposed, and no proposals will be carried over into the next cycle.
  • There is a cap for VLBI of 5% of ALMA Cycle 8 observing time.  As time for GMVA observations will thus be scarce, proposals should include a quantitative justification as to why ALMA is essential for the goals of the project.

 Resubmission of ALMA Cycle 7 proposals:

The outcome of scheduled GMVA+ALMA Cycle 7 observations scheduled in April 2020 is unlikely to be known until after the ALMA Cycle 8 proposal deadline.  If the PI wishes to mitigate against the possibility that these observations are not completed successfully, the proposal must be resubmitted to ALMA by the Cycle 8 proposal deadline and undergo a new review. The proposal does not need to be resubmitted to the GMVA in this case.  Observations in Cycle 8 will only occur if the April 2020 observations are not completed successfully and the ALMA Cycle 8 proposal is ranked high enough for scheduling.

However, if the PI wishes to obtain a second epoch of GMVA+ALMA observations, even if the April 2020 observations are successful, a new proposal must be submitted to both the GMVA and ALMA by their respective proposal deadlines.

Documentation and Assistance

Detailed Information about the VLBA instrument, its capabilities, observing strategies,  proposal preparation and submission, and  observation preparation, can be found in the VLBA Observational Status Summary, at the Guide to Proposing for the VLBA, and at the Observing with the VLBA  web pages. Answers to Frequently Asked Questions are contained in these proposing and observing guides. Questions may also be directed to the NRAO Helpdesk.

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