VLAPEAK

VLAPEAK is used to control reference pointing on the VLA. The user will need to provide a scan of at least 2.5 minutes on a calibrator on which the pointing can be done. The observations should be at X band. These scans can be inserted explicitly, or AUTOPEAK can be used to insert them automatically (maybe not yet). SCHED will create appropriate INTENTs for the VLA scans based on the value of VLAPEAK. It is not recommended that the user attempt to specify the pointing related INTENTs explicitly although that is not prevented. If that is done, there can be interactions with the defaulting when other, unrelated INTENTs are used.

The four settings for VLAPEAK situations of interest are:

'DETERMINE' indicates that the reference pointing corrections should be determined starting from no offsets. This sets INTENT = VLA:REFERENCE_POINTING_DETERMINE

'APPLY' indicates that the most recently determined reference pointing offsets should be applied. This sets INTENT = VLA:REFERENCE_POINTING_APPLY

'ADJUST' indicates that reference pointing corrections should be determined starting with the previously determined values. The results that can be applied to later scans are the sum of the previous and the newly determined values. This sets INTENT = VLA:REFERENCE_POINTING_ADJUST

'OFF' indicates that no reference pointing offsets should be applied and that no attempt should be made to deterimine them. This is the default and is what will be used at all but the highest frequencies. This sets INTENT = VLA:REFERENCE_POINTING_OFF

A pointing pattern can be done if in a scan if there are at least 150 on source. Only one pattern is done, so adding significantly more time is not useful (unlike the old VLA system).

Reference pointing is important for observations at 1cm (K band) and higher frequencies (ie Q band). It might be useful at the high end of the 2cm (Ku band) range. For more information about reference pointing on the VLA please see the Guide to Observing with the VLA section on High Frequency Observing Strategy. The pointing should be done at C or X band, with X band recommended.

VLA reference pointing and array phasing must not be attempted in the same scan. SCHED will abort if that is tried.

• Argument: Text of up to 9 characters.
• Options: See list above.
• Default: 'OFF'.
• Usage: Defaults to previous scan.
• Example: VLAPEAK='APPLY'