High Sensitivity Array (HSA)

by Emmanuel Momjian last modified Dec 01, 2020 by Justin Linford

High Sensitivity Array

For projects that require the maximum sensitivity, users should consider submitting proposals for the High Sensitivity Array (HSA). Currently, users may add the following telescopes to the VLBA to improve sensitivity:

  • Effelsberg: Effelsberg has often been used in conjunction with the VLBA, and is frequency agile at 5 GHz and above. For more information about including Effelsberg with the HSA we refer to the Effelsberg HSA page and the Effelsberg VLBI page.
  • Green Bank Telescope: The Green Bank Telescope is also commonly used with the VLBA, and is frequency agile (with some limitations) at all its bands.  See the VLBI at the GBT page for more information.
  • Very Large Array:  The Very Large Array (VLA) is available in phased-array mode (Y27).  Please see the VLBI at the VLA, and the HSA/GMVA/Global VLBI and Building a Schedule chapters of the Guide to Observing with the VLBA pages for further considerations.

Check the OSS for any limitations or special instructions for each HSA telescope.  Also, make sure to use the EVN sensitivity Calculator to estimate the rms noise for your observation.

Special considerations for HSA proposing and observing

  1. Proposals: Proposals should be sent to NRAO only, through the Proposal Submission Tool, which can be accessed via NRAO Interactive Services. Click on VLBA/HSA when creating the proposal.
  2. Field of View:  The field of view of the HSA is more limited than for the VLBA, because of the smaller primary beams of all the HSA telescopes, especially the phased VLA (Y27). For the latter, note that the larger the extent of the array, the smaller its field of view.    
  3. Scheduling: Use NRAO's SCHED software to make the observing schedule, available from anonymous ftp at: ftp.aoc.nrao.edu The SCHED manual has several example files to get you started. Please be sure to use the latest version of the software, or to run SCHED on the final schedule file submission.

    For scheduling note that:
    • Effelsberg has station name 'EB_VLBA'
    • GBT has station name 'GBT_VLBA'
    • The phased VLA has station name 'VLA27'
  4. Slew speeds:The Effelsberg, GBT, and VLA slew speeds are slower than for VLBA antennas. The GBT slew rate also decreases during cold weather.  Be aware of this when writing your schedule, and be sure to examine the output from SCHED. SCHED has the latest information on slew speeds, including acceleration and deceleration, for all telescopes.
  5. Pointing: Since the Effelsberg and GBT antenna beamwidth is ~4 times smaller than those of VLBA antennas, periodic pointing checks are essential, especially during short wavelength observations. Observers should leave frequent gaps in their VLBI schedules (~10 mins each) to allow the telescope operators to make these checks. They should be about every hour or two at 4cm, and more frequently at shorter wavelengths. See the VLBI on the GBT page for more specific information on how and when to schedule pointing checks.
    The VLA also requires pointing at frequencies lower than the VLBA, for the VLA however the pointing must be scheduled by the observer in SCHED.  See VLBI @ the VLA:Scheduling Hints for examples more information.
  6. Submitting Schedules: The submission deadline is two weeks before the observation. The input file for SCHED, incorporating any non-standard setup files, should be e-mailed to vlbiobs@nrao.edu.  If you have problems with your schedule contact vlbiobs@nrao.edu If any changes are made to schedule after the deadline the support personal at all the telescopes must be contacted.
  7. Frequencies: While the GBT has frequency coverage equal to the VLBA, changing receiver bands takes 5-10 minutes. For more details on changing frequencies at GBT see the VLBI on the GBT page.
    The VLA and VLBA have similar frequency bands, but the VLA receivers generally have a wider tuning range.
    See Instructions for Joint VLBA + Effelsberg Observing for information about frequency availability and changing between frequencies at Effelsberg.
  8. Non-Standard Frequency Setups: Observers using non-standard frequency set-up files (i.e. not one supplied with the current version of SCHED) should contact the technical friends at the telescopes. These are Frank Ghigo at the GBT and Uwe Bach at Effelsberg. Contact should be made well before the observations so that any special files needed for tuning can be made in good time.
  9. Correlator: All observations will be correlated at the VLBA correlator in Socorro.
  10. Archive: All observations will be archived on-line and password protected during the 1 year proprietary period. Request a project access key from the data analysts. See the NRAO data policy for further details.

 

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