Current Restrictions

You have reached an obsolete page. For the latest version, please go to the appropriate section in the VLA Observing Guide.

New: 08/15/2012: Scheduling blocks can now be a multiple of 0.25 hours (15 minutes) in total duration. For example: 00:30:00, 00:45:00, 01:15:00, 01:45:00, 02:00:00 etc.

New: 07/31/2012: The scan length limit is now 10 minutes for any hardware setup. CASA can now handle longer scans, therefore the 90sec x integration time limit has been lifted.

New: 05/08/2012: Problems affecting observations requiring Stokes V, spectral line, have been solved and observation of such projects has resumed.

When preparing scheduling blocks, observers should be aware of restrictions currently in place. We expect we will be able to lift some, and introduce others, so always consult this page when preparing scheduling blocks.

Scheduling Block (SB)

All scans must be scheduled in LST duration, and the total length of an SB must be a multiple of 15 minutes.
Every dynamically scheduled SB must specify an LST start range, which is the range of possible start LST times for this SB; not the total LST span of the SB (all is an option for circumpolar sources)
Under the Reports tab, we recommend stepping through a number of representative LST start times, to make sure all sources are above their elevation limit and have enough time on source at all times. Operators cannot interfere with an executing script, and requests to ensure enough time on a certain source in e.g. Comments to the Operator cannot be honored
Every dynamically scheduled SB must specify dynamic constraints (wind/API)

Resource Table

Frequency type has to be Sky, unless Doppler Setting is being used. To schedule sources that require more than one Doppler Setting resource, you must include a dummy scan of at least one minute on each individual resource at the beginning of the SB (much like the first dummy scan below), and remember to include at least one bandpass calibration scan using each of these Doppler Setting resources (see Scan Table restrictions below)
Referenced pointing scans (scan mode=Interferometric Pointing) always require a one second integration time. For all other kinds of scans there are lower limits, which are also the default. In the D- and C configurations these are 5 seconds for L, S, and C bands, and 3 seconds for the higher frequency bands. In the B-configuration it is 3 seconds for all bands, and in A-configuration 1 second for all bands.

Source Table

There should be at least one standard flux calibrator scan per band (3C48/3C147/3C286)
The resulting on-source time (as it must be scheduled in LST duration for dynamic scheduling) for this calibrator must be more than 30 sec

Scan Table

Assuming you have a single target frequency, the first scan must be a dummy scan of at least 1 minute duration, and with a resource set up like the second scan. It is recommended to name this first scan dummy. The second scan is the first real scan; for high frequency observations with pointing the fourth scan is the first real scan (see below). Dummy scans do not need a valid 'on source' time in case the OPT warns you about that, and if you use multiple target frequency setups you need to include a 1m dummy for each frequency setup used at the beginning of the SB with the hints as described above. The first real scan number moves one up with each additional dummy/frequency setup. there is currently no need for dummies elsewhere in the SB. For the dummy scan at the referenced pointing frequency use 'Scan Mode' = 'Standard Observing', not 'Interferometric Pointing'!
The combined duration of the dummy scan and the first real scan should be around 10 minutes, not less. If your integration time requires shorter scans, repeat that shorter scan enough times for the total to add up to 10 minutes. If you are scheduling pointing scans at the beginning (for high frequency observing, K, Ka and Q bands) you should plan to extend the startup to about 12 minutes to allow sufficient time for valid pointing solutions to be derived (see below)
The first real scan and the last scan must be scans on a calibrator
Every SB needs at least one scan with CalFlux intent
Every resource needs at least one scan with CalBP intent
Every target with a different resource (frequency) needs to be bracketed by calibrator scans using that same resource if it is uncertain that self-cal will work
Every calibrator scan needs at least a CalGain intent
Polarization observations need CalPolAng and CalPolLeak intents
For OSRO modes, the maximum scan length is 10 minutes, that includes slew and on source time. If longer on-source scan lengths are needed, use a loop containing several scans each of legal duration.
When scheduling SBs which require referenced pointing (for high frequency; over ~18 GHz), please use the following starting sequence (for one target frequency):

1 min dummy at target frequency
1 min dummy using a pointing default (typically C or X band in OSRO1)
10 min pointing (minus a minute for every extra dummy inserted for other bands prior to the pointing scan)
your first real scan

where all dummies are the same source as your pointing source and the dummies and pointing for 12 minutes will assure enough time for slew and pointing solutions. No dummies are needed after this sequence and additional pointing scans, necessary when the Az/El of the sources differ more than about 15-20 degrees from the last pointing direction, only need durations sufficient to cover the total of slew time and 2.5-3 minutes of actual pointing (i.e. 2.5-3 minutes on-source). Note that switching to a pointing scan usually introduces a correlator change, which currently should trigger adding an extra 30 sec to the pointing scan and the scan following it (see next item). Finally, for the dummy scan at the referenced pointing frequency use 'Scan Mode' = 'Standard Observing', not 'Interferometric Pointing'!

When the correlator setup changes, always add 30 seconds to the regular time of that scan in order for the requested change to take effect. A common case is when a reference pointing scan uses a wider bandwidth than the following source scans, but there are other examples as well. Note: a band change without changing the correlator setup does not constitute such a change and no additional 30 seconds are needed in that case, except for changing in and out of X (and Ku) band which use the opposite side band from the other receiver bands. Thus for pointing in X band to observe in K, Ka or Q band, this extra time is needed.

No tipping scans
By going through possible LST start times and assuming unknown or specified wrap, make sure there is at least 20 seconds on source for each calibration scan and 2.5 minutes on source for each C band pointing scan, 3 minutes for X band pointing scans (see above under correlator changes)
If your source list includes sources with Declination larger than about 34 degrees, it is recommended that you specify the antenna wrap for the scans where it may matter (typically set for the first few scans). See Appendix A of the OPT manual

Verification

Make sure the SB verifies and is error-free before submitting. Until you do so the submit button will not work.