FAQ

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JCMT OT

Normally a repeat counter is not necessary. A single MSB should be between 30-70minutes in length. To build up the total time require on a source you should increase the “Observe Counter”. A repeat counter may be used when performing a Heterodyne stare observation. In this case it may be ideal to have each stare last ~15-20minutes and use the “repeat” counter to produce a sensible MSB length.

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Observers usually base a reference/off position on knowledge about a region/source from previous data or information from the literature.

If you are unsure of your reference position you might want to add a quick 5 minute stare observation of your reference position in the same set up as your science observation. You can then add to the notes that the science observation must only be taken if the reference position is clear.

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Use what you need. i.e. only request wideband mode if your source requires it. Only request multi subband observations if you need it and not to get “free lines” – typically the more complex an ACSIS set up the higher the chance for baseline issues due to less stable power supplies. Choosing two 250 MHz bands with lines in the center of each band is better than choosing a 400 MHz band centered on one line.

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A basket weave is an observation in which one scan ha a “Scan PA” component set to “Along Width” and a second scan has the  “Scan PA” set to “Along Height”. If you are mapping a small region you can simply do this within the same MSB. To do this copy the scan component and paste it below the original scan component and adjusting the “Scan PA” accordingly. You might also need to update the Sample Time to ensure your MSB remains a sensible length.

For larger scan areas (>0.5 degrees in size) you might have to have a separate MSB for the “Width” and “Height” due to the total length. If this is the case it is recommended you request in the notes that two observations are taken back to back to ensure an even coverage in terms of sky transmission (in terms of elevation and weather).

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Do not edit an older copy you have on disk and upload.
In JCMTOT click on Fetch Program to retrieve the MSB’s from the database. Then do any necessary modifications and Store to the Online Database. This will prevent repeating observations which already have been done, and keeps modifications done by your FoP.

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Heterodyne: The aspect of the MSB (Minimum Schedulable Block) you most want to think about is its length. If you have been allocated e.g. eight hours for a single source, you could submit a single 8-hour MSB if you wanted. But that would be a very silly thing to do. If your source is not up for more than eight hours, it would never be scheduled as our software would detect that it would set before the MSB could be completed. But even if your source were observable for 8 hours solid, the observer won’t choose to undertake it except near the very beginning of the night, which vastly decreases your scheduling opportunities.

On the other hand, if many short observations are all scheduled one after the other they would have to be sent to the queue one by one, thus driving the TSS and observer insane.

If your sources are well separated across the sky a pointing will be required between them (even if they are only separated in time by ten minutes). However if they are close by each other they can be done consecutively. If you are including multiple sources in an MSB try to pair or group them so they are all are all close together. If this is not the case then include an note highlighting this to the operator.

The golden mean? A 30-to-90 minute MSB. If you have any questions about the best way to distribute your sources please consult your Friend of Project for ideas.

SCUBA-2: We have a 40 minute limit on SCUBA-2 observing blocks. This upper limit usually concerns large pong maps while small daisies fall at the other end of the scale being potentially only a few minutes each. Having short MSBs for SCUBA-2 does not incur the same overheads as heterodyne. Like heterodyne observation consecutive sources that include a large slew will likely require a pointing between them, however SCUBA-2 has the additional factor or requiring the arrays to be setup again after a move between sources.

 

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There isn’t one. However if you don’t submit MSBs for your sources by the time they are observable you could be throwing away opportunities of having your sources observed. Nevertheless, note that there is no requirement that you submit your entire project at once. Therefore you can submit some MSBs, wait for them to get done so you can analyze the results and then submit other MSBs to follow up on those results. Your MSBs will keep on being scheduled until you have exceeded the total time allocated to your project.

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You probably forgot to enter your co-ordinates! If you really meant to observe 0:0:0, 0:0:0 just ignore it.

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You certainly can. However I suggest you let us know for two reasons. First, for your benefit, we’ll be able to look your MSBs over to ensure that they will actually do what you intend. Secondly, for our benefit, we would like the chance to create a library MSB that matches your observing mode in case that will be useful to other users.

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We would rather you did not. Your Friend Of Project will not enable your program for observing until they are sure the construction is good. Uploading to the database is the best way to work with us, and get help. Upload it and then notify your F.O.P. so they can review it and suggest or make changes. Also there is a risk with xml sent via email that the lines are not wrapped – this will produce illegal xml.

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