Observing with the High Sensitivity Array

Proposing and scheduling the HSA should be almost as easy as using the stand-alone VLBA, but there are some unavoidable complications that accompany the additional antennas. The purpose of this document is to alert the HSA user to these complications and suggest ways to deal with them.

1. Instructions for doing VLBI at the non-VLBA telescopes:
   • Effelsberg: Instructions for Joint VLBA + Effelsberg Observing
   • Phased VLA: Very Long Baseline Interferometry at the VLA and Guide to Observing with the VLBA: HSA/GMVA/Global VLBI
   • GBT: VLBI on the GBT
2. 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.
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. 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 the support personal at all the telescopes must be contacted.
   • For the VLBA and the phased VLA notify vlbiobs.
   • For the GBT notify Pedro Salas and Toney Minter.
   • For Effelsberg notify the Observing Friend.
7. Frequencies: While the GBT has frequency coverage equal to the VLBA, changing receiver bands takes 10-15 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 the technical friends at the telescopes. These are Pedro Salas 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. See the NRAO data policy for further details.