The VLA can be split up in subarrays. That is, a subset of the 27 antennas and corresponding baselines can be ordered to do a completely different and independent program than other antennas. This may be the case when an observer has asked to divide up the array for a single project to observe a source simultaneously in multiple bands, to observe multiple different sources simultaneously that do not need the full array, or when one antenna is split off from the main array for inclusion in a VLBI array by another user (i.e., Y1).

The current restrictions for observing with subarrays are:

  • The use of subarrays has to be requested in the proposal and approved by the TAC.
  • Up to 3 subarrays may be used. Note that the array cannot be divided up in three equal subarrays of nine antennas. For instance, three subarrays may be obtained by having 10 antennas in subarray 1, 9 antennas in subarray 2, and 8 antennas in subarray 3. For more information and for other possibilities see the subarray configuration details in the VLA OSS.
  • Until further notice, only 8-bit default NRAO wideband continuum frequency setups may be used for standard interferometric observing (no phasing, binning, etc). Other modes may be offered as RSRO in the call for proposals.
  • The division of observing directions, frequency bands, polarization products and integration times over subarrays is unrestricted. However, each subarray can only use only a single correlator setup during an observation, i.e., changing the correlator setup even for reference pointing is not allowed. The latter restricts the observing frequencies to the lower frequency bands of the VLA. OTF modes are not supported in subarray observations.
  • Only a single scheduling block should be submitted through the OPT, with appropriate comments to the operator. This scheduling block should consist of Subarray Loops, one per subarray in which separate lists of scans are placed for each subarray. Each Subarray Loop defines the antennas used per subarray. Check the OPT manual before you start making the subarray schedule by referring to the Subarray Observing section.
  • The sum of data rates and other restrictions and guidelines for standard (single subarray) observations must be taken into account.
  • All Subarray Loops in a single Scheduling Block are started at the same time.

Please the Subarray Observing section in the OPT manual for further information or contact the NRAO Helpdesk.