25B TAC Report

Summary

A total of 287 proposals were submitted to NRAO's North American facilities for semester 25B.  These include the Robert C. Byrd Green Bank Telescope (GBT), the Very Long Baseline Array (VLBA)/High Sensitivity Array (HSA), and the Karl G. Jansky Very Large Array (VLA).  Proposals are reviewed on a competitive basis with a panel review system (see Proposal Review System).  Below are the statistics by proposal count and hours.  The oversubscription is the ratio of the number of submitted proposals to the number of approved proposals.  The pressure is the ratio of the requested time to the available time in hours.  Here we only include proposals submitted for the 25B semester that have been reviewed by the NRAO TAC.  We count HSA proposal hours that request the GBT or VLA as a VLBI station.

Statistics by Proposal Count
Proposals GBT VLBA VLA
Submitted   53   70 164
Approved   31   33   62
Filler     6   16   41
Rejected   16   21   61
Oversubscription   1.7   2.1  2.6
 
Statistics by Proposal Hours
Proposals GBT VLBA VLA (B)
Requested 6472.83 1814.8 4754.22
Available 1931.77    593.0 1743.00
Approved 2035.50    584.9 1624.00
Filler   134.00    337.9   939.09
Rejected 4155.08    891.9  1985.93
Pressure    3.4       3.1     2.7
 

For the 25B semester, the NRAO had agreements with ALMA, the James Webb Space Telescope (JWST), the Hubble Space Telescope (HST), the Swift Gamma-Ray Burst Mission, the Chandra X-ray Observatory, the XMM-Newton Telescope, the Neutron Star Interior Composition Explorer (NICER), and the Imaging X-ray Polarimetry Explorer (IXPE) to submit joint proposals whereby the NRAO TAC could allocate time on these external facilities (see the 25B Call for Proposals).   The table below summarizes the results for all AUI North American facilities that are included in the joint program: GBT, VLBA, and VLA.  The time available on the external facilities is per year, whereas the time requested and approved is only for semester 25B.

 

Joint External Proposals

ALMA

(hrs)

JWST

(hrs)

HST

(orbits)

Swift

(ks)

Chandra

(ks)

XMM

(ks)

NICER

(ks)

IXPE

(ks)

Available

 50.00 50.00 30 300.0 120.0 150.0 250.0 300.0
Requested 75.37 51.51 12   22.5   10.8 173.0   72.0   30.0
Approved 25.60 17.71 12   22.5    0.0   72.0     0.0   30.0

 

 

Telescope Pressure Plots

Pressure plots show the total hours of allocated time as a function of LST (or GST).   Also shown are how the hours are divided with respect to weather conditions and observing priority.  Click on the plot to enlarge. 

GBT

GBT pressure plot as a function of LST.  There are three weather categories: excellent weather (18 − 26.5 GHz and > 50 GHz; top-left), good weather (8 − 18 GHz and 26.5 − 50 GHz; top-right), and poor weather (< 8 GHz; bottom-left). The bottom-right panel includes all weather categories. The gray line shows the total hours available.

GBT Pressure Plot 25B

 

The following heuristics were used to generate the initial scheduling priorities for all sessions that are subsequently used by the TAC to derive the final recommended priorities.

  •  Priority A. Must have a linear rank between 0–5.0 and meet the following conditions.
  1. No more than 90% of the LST time has been taken by carry over and other A projects in the appropriate
    weather categories.
  2. Fixed, windowed, elective, and triggered observations must have good and excellent weather time
    available. These projects will count 25% of their time against the total good weather and 25% against
    excellent weather high frequency time as we cannot guarantee that the projects can be scheduled solely
    in poor weather conditions.
  3. Fixed, windowed, elective, and triggered observations cannot exceed 90% of the good weather total
    time and 90% of the excellent weather total time at any LST hour.
  4. Excellent weather high frequency time (Mustang2, ARGUS, and W-band non-VLBI) cannot exceed
    the available night time hours at any LST hour.
  • Priority B. Must have a linear rank between 5.001–7.50 and meet the following conditions:
  1. No fixed date observations. We can still do electives (multiple chances) but they will only be scheduled
    under the correct weather conditions (e.g., a triggered poor weather project would not be scheduled in
    good or excellent weather).
  2. Monitoring observations are not given windowed periods with guaranteed observations. They must
    use project unavailable times or enable/disable sessions to perform pseudo-monitoring.
  3. The time cannot exceed the available time or the available night time hours by more than 125% in any
    LST hour.
  4. Any proposal exceeding the 125% threshold would be given a lower priority.
  5. No excellent weather projects will be accepted for this priority.
  6. No triggered observations will be accepted for this priority.
  • Priority C. Must have a linear rank beteen 7.501–10.0.
  1. All priority C time will be considered filler time.
  2. No excellent weather high frequency time will be given a priority C.
  3. There will not be any limit on the amount of time accepted as a priority C.
  4. No fixed, elective, triggered or monitoring observations will be accepted as a priority C.
  • Priority D. Will be for filler calls or extraordinary circumstances.

VLBA

VLBA pressure plot as a function of GST. The black line with squares is 68% of the wall-clock time available (after removing time for maintenance and sponsored time). The VLBA has two weather categories: high frequency (above 12 GHz, light shading) and low frequency (below 12 GHz, dark shading). The colors correspond to pre-committed time (brown), priority A (green), priority B (yellow), priority C (red), and priority N (blue).  The shading within each priority indicates high frequencies (lower on the column) or low frequencies.

 VLBA Pressure Plot 25B

 

The following heuristics were used to generate the initial scheduling priorities for all sessions that are subsequently used by the TAC to derive the final recommended priorities.  Additional constraints for high frequency are in italics.

  • Priority A.
  1. Linear rank ≤ 2.5.
  2. Less than 48% of the time available for scheduling (total time available minus pre-committed priority A time).
  3. Less than 75% of the total time available for scheduling (including pre-committed priority A time).
  4. Less than 75% of the high frequency time available for scheduling (including pre-committed priority A high frequency time).
  •  Priority B.
  1. Linear rank ≤ 5.0 (or ≤ 6.0 for pressure without < 80% available for priority B).
  2. Less than 96% of the time available for scheduling (total time available minus pre-committed priority A and B time).
  3. Less than 100% of the high frequency time available for scheduling (including pre-committed priority A and B high frequency time) and linear rank ≤ 5.0.
  • Priority C.
  1. Linear rank ≤ 7.5 (or ≤ 9.0 for pressure without < 80% available for priority C).
  2. Less than 150% of total time available.
  3. Less than 125% of the high frequency time available for scheduling (including pre-committed high frequency time) and linear rank ≤ 7.5.

 

VLA

VLA Pressure plot as a function of LST. The VLA has two weather categories: high frequency (above 12 GHz, light shading) and low frequency (below 12 GHz, dark shading). The figure below show the pressure for the B-configuration.  The black lines indicate the total time available for science (solid), the time available for K-band and higher frequencies (dashed), and the time available for Q-band (dotted).  The letters A, B, C, and N correspond to the scheduling priorities where A and B are approved time, C is filler time, and N is rejected time.


 VLA Pressure Plot 25B (B)

 

The VLA Prioritizer is software that generates the initial scheduling priorities for all sessions that are subsequently used by the TAC to derive the final recommended priorities.  The TAC can and does change the priorities suggested by the Prioritizer. Also note that sometimes the Prioritizer cannot follow these rules strictly because of the composition of the proposals submitted.  For semester 25B, the following rules were adopted as input to the VLA Prioritizer:

  • Priority A is only to be considered for the top quartile of proposals.
  • Priority A is only assigned if it can be given to all sessions of the proposal.
  • Priority A should not to exceed 60% of available time at any LST.
  • Priority (A+B) should not to exceed 92% of available time at any LST.
  • Priority B should not to exceed 80% of available time in any 3h interval.
  • Q band sessions will be given priority C only if linear rank is less than 1.0.
  • Ku, K, Ka-band sessions will be given priority C only if linear rank is less than 3.5.
  • The goal for priority C is to assign 120% of available time.
  • Proposals rated worse than 9.7 will not be scheduled.

 

Observation Preparation

GBT

Please use the GBT Dynamic Scheduling System (DSS) to enable observing sessions, select observers for your project, and enter your blackout dates. The DSS Home Page has additional information about the DSS. See GBT Observing for information about how to prepare for your observations.

Please note that the DSS uses the average Right Ascension (RA) and Declination (Dec) of all sources within a session. The average RA and Dec will be used to determine when the session can be scheduled. You will need to carefully check the RA and Dec, along with the minimum and maximum session lengths, to make sure that these values are satisfactory and will allow all your sources to be observed before enabling the session.

VLBA

Unless otherwise stated in the TAC comments, proposals approved for priority A time will be eligible for scheduling in semesters 25B and 26A, and proposals approved for priority B or C time will be eligible for scheduling only during semester 25B.

IMPORTANT: Schedule (.key) files for proposals allocated time in the VLBA dynamic queue should be sent to vlbiobs@nrao.edu by the start of the semester (August 1, 2025); proposals with fixed-date allocations (e.g., HSA proposals) should also submit schedule (.key) files by this date to facilitate scheduling of their observations.

For advice on preparing your scheduling blocks, please see the VLBA Observing Guide or use the helpdesk.

VLA

Unless otherwise stated in the TAC comments, proposals approved for priority A will be considered for scheduling for two VLA configuration cycles, and proposals approved for priority B or C time become ineligible when the associated configuration ends.

IMPORTANT:  The tentative start dates for the B-configuration is 3 September 2025.  Projects will be made available and a reminder will be sent approximately one month before the start of each configuration. Users granted dynamic, non-triggered time, must either submit their scheduling blocks before the start of the configuration or contact the VLA Scheduler (schedsoc@nrao.edu) before that date to avoid a reduction in scheduling priority. Configuration
plans are available at:Configuration Plans.

In semester 25B, for B configuration daytime maintenance activities peak at about 14:00 hours LST, so the available observing time is least in and around this LST. For status of the VLA and links to the monthly schedules
please see the schedsoc home page.  For advice on preparing scheduling blocks, please consult the VLA Observing Guide or use the helpdesk.

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