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Advanced Topics

A note about placement

For example, look at the example below of a Science Program containing three MSBs - focus on the location of the two Site Quality components:

What does this mean? The first Site Quality component is on the same level of indentation, and therefore the same level of branching, as the MSBs. If that was the only Site Quality component present it would apply to all MSBs in the Science Program. As it is, the first MSB has a site quality inside it (technically: within its scope). So the first MSB will be scheduled using the criteria of the Site Quality component inside it, and the second and third MSBs will use the first Site Quality component since they lack one of their own. The technical term for this behaviour is "inheritance" for those familiar with it already.

Common uses for inheritance are e.g. to place the Het Setup outside the MSBs if you want to observe multiple sources at the same frequency. Conversely, the Target Component can be placed outside multiple MSBs are needed on the same target. However, carefully read the next item on the interaction of the Het. and Target component.

See the section on "AND and OR Folders" on how an AND folder can be used to group observations and use inheritance within that group.

Velocities: The Het and Target Component.

Hence the OT now allows for the observing velocity to the specified in the Heterodyne Component or the Target Component. But this has made life a bit more complicated.

The description of the Heterodyne Setup component should have made it clear that it uses the velocity to compute the approximate sky frequency as a check whether the line falls within the tuning range, to show the setup in the frequency editor etc. However, it can only do that if it has access to the velocity information. In the case where the velocity information has been put in the Target Component, this requires the components to be at the same level of indentation. If this is not the case, the Het. Component will assume a velocity of 0 km/s.

Note that is only a problem within the OT: when MSBs are submitted for observation the tree structure from the OT is unrolled and for each observation the appropriate Het Setup and Target Component are paired up.

In general, this is not a problem for Galactic sources since the overall parameters of the observation of a molecular line (center frequency, atmospheric transparency, receiver characteritics) don't significantly differ from source to source. That of course may not be the case for extra-galactic and high-z sources: vary the velocity or red-shift enough and the line may shift completely out of the band or into an atmospheric absorption line for some of the sources (it has happened!). The Het. Component will notify you of (un)available transitions for a particular molecule and the Frequency Editor will show the transmission at the observing frequency, but only if it can find the velocity of the observation.

Small print: which is one of the reasons that we advice to always select a 'Molecule' and 'Transition' from the drop-down list, rather than typing a frequency manually.

In summary, the following sample layouts allow for the Het. Component to obtain the velocity from the Target Component:

    *MSB                           *MSB                           *AND                      
      o Het Setup             	     o Site Quality                 o Het Setup             	 
      o Site Quality           	     o Observation                  o Site Quality           	        
      o Target Information             - Het Setup                  o Target Information
      o Observation                    - Target Information         o MSB1            
        - Sequence                     - Sequence                     - Observation    
           ...                            ...                            + Sequence
                                                                           ...
                                                                    o MSB2
                                                                           ...

    *MSB                           *MSB                           *AND                      
      o Het Setup             	     o Site Quality                 o Het Setup             	 
      o Site Quality           	     o Target Setup                 o Site Quality           	        
      o Observation                  o Observation                  o MSB1              
        - Target Information           - Het Setup                    - Target Information
        - Sequence                     - Sequence                     - Observation    
           ...                            ...                              ...
                                                                    o MSB2
                                                                      -  Target Information
                                                                             ...

Generating a programme from a catalogue file

Start with a science program which contains the template MSB that you wish to use for the replication, but LEAVE THE NAME AND COORDINATES IN THE TARGET COMPONENT BLANK (for example, a template MSB you have retrieved from the ACSIS library). Your catalog file should be of the format:

PKS0106         01 08 38.771 + 01 35 00.32 RJ
3C84            03 19 48.160 + 41 30 42.10 RJ  
3C120           04 33 11.096 + 05 21 15.62 RJ
PKS0438         04 40 17.180 - 43 33 08.60 RJ

Under the edit menu, there is an option called "Replicate from catalog". Choose this action:

A file selector window will pop up which allows you to choose the location of the catalog file. Once you have done this, the OT will contact our site and after a short delay will pop up a new science programme window containing multiple MSBs. So if you had an MSB with one blank target component and a catalog file with 12 sources, you will get back a science programme with 12 MSBs, whose target components have been filled in using the information from your catalog.

Of course you may have to tweak the MSBs further, such as giving them more informative titles and tweaking the number of integrations on each source. It is also not yet possible for the source replicator to insert source velocities from the catalog into the MSBs.

Additional Scheduling Constraints

The scheduling constraints component allows you to:

• specify a specific time window in which you want your observations to be taken. Needless to say setting this too narrowly will reduce your chances of being scheduled, so only do this if there is a valid scientific reason

• set a rescheduling action, that will schedule an MSB that has been completed to reappear after a certain number of days. If you have been allocated time for a project that requires periodic monitoring, you may wish to ask us for more information on how this works.

• by default, a target is considered observable if it is between 30 and 88 degrees of elevation for the entire duration of its MSB. If you wish to specify a lower elevation criterion (eg. for a very low or very high declination source) you may do so here.

• restrict a target to being observed only before or after transit. Again, note that this criterion will be applied for the entire estimated duration of the MSB, so only do this if it is scientifically vital.

OR and AND Folders

An OR folder can contain N items, and you can set the "Select" counter on the OR folder to indicate that you'd like any subset of size M to be observed. For example, if you wanted to try to detect the CO line in an object, but were not concerned in which transition (either 3-2 or 2-1), one could use a top level OR folder which contained a target information component and two MSBs as shown below. The user should set the "Select" counter of the OR folder to 1 to indicate that just 1 of the MSBs should be executed (not both).

Another application of OR folders is managing available telescope time for projects with a large number of potential targets. Suppose an observer wants to observe from a sample of 40 potential targets. Further suppose that some of the objects will require follow up observations towards the end of a semester and telescope time is somewhat limited (i.e. not enough to observe them all once and follow up the interesting ones). One solution would be to put the 40 MSBs for the sample into an OR folder, then set the "select" switch to, say, 10 objects. This will mean that no more than 10 objects will be observed from the sample. This can be used to ensure that all of the telescope does not get used up in making first observations, and that some time will be left over for follow up observations. This kind of programme management can involve the observer, in conjunction with the support astronomer, dynamically altering the programme in the light of past observations, results of data reduction and available telescope time.

An AND folder does not influence the availability of its contents, as an OR folder can, once an MSB inside it has been observed. Instead, they simply enable observations to be grouped together. In the example below, AND folders are used to indicate that the observer would prefer to end up with observations A and B or X and Y rather than A and X and A and Y. The order of observations, and which get done, will still depend only on project priority, source availability and weather. If the observer absolutely needs two targets observed to get any meaningful scientific result, they should go in the same MSB rather than in an AND folder - do not forget MSBs are allowed to contain multiple targets.

An alternative use for an AND folder is to avoid having to reproduce information that is common to several MSBs - the site quality, Target info, and/or Het Setup for example. An individual component can be pulled out of the MSBs and set into the hierarchy at the AND folder level. In the following example, we have been allocated both bands 1 and 2 for our project; however, because of differences in their expected fluxes we want to observe targets A and B in band 1 and targets C and D in band 2.

Survey Container

The survey container is an extremely useful tool when you want to carry out the same type of observations of a large number of sources. It works similar to the replication example above, but it does not replicate the MSBs in the OT, only in the database. I.e. a single observation for a target list with 100 sources will have 1 MSB in the OT, but 100 MSBs in the database after uploading your science program.

{This section will be updated at a later stage when the input file format for ACSIS has been finalized.}

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