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Control and Performance
One panel at the top of the page shows array and telescope configuration information. This should be used to guide a user in the choice of parameters in the panel below, that control predominantly the time required and whether the ACA is required.
Figure 5.9:
The Science Goal Control and Performance parameters.
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The configuration information (all calculated assuming the sky-frame equivalent of the Representative Frequency for the first source in the Science Goal) are:
- Antenna Beamsize: Display of the antenna beam size for the 12- and 7-m dishes.
- Number of antennas: The number of baselines assumed for each of the arrays. As the 7-m and TP array times are actually based on the times required for the 12-m configuration, only the number of 12-m antennas has any practical effect on the OT's operation. These numbers are set by default in the ALMA Sensitivity Calculator.
- Longest baseline: The maximum baselines available for the most compact and extended 12-m array configurations. For the two highest bands (8 and 9) the largest configuration is not available.
- Synthesized beamsize: The synthesised beam sizes for the corresponding maximum baselines.
- Shortest Baseline: The minimum baselines available for the most compact and extended 12-m array configurations. For the two highest bands (8 and 9) the largest configuration is not available.
- Maximum recoverable scale: The largest structures that it is possible to image with the most compact and extended configurations.
The user-entered parameters are the following:
- Desired Angular Resolution: The desired angular resolution (synthesized beam size). Must be between the best resolution achievable (i.e. with the most extended configuration) and twice that achievable with the most compact configuration. The latter allows a modest amount of smoothing during data reduction. Based on this value, the OT will choose an appropriate 12-m array configuration. If this is one of the more extended configurations, it is possible that a second 12-m configuration might be selected, depending on the largest structures that need to be imaged.
- Largest Angular Structure in source: The angular extent of the largest components in the source that need to be imaged. This parameter (also sometimes referred to as the Largest Angular Scale) sets whether more than one 12-m configuration is required. Potentially, multiple 12-m configurations, the ACA 7-m and Total Power arrays might be necessary to reliably image the indicated size of the source structure. Point Source should only be selected if the target(s) will be unresolved in even the largest available configuration.
- Desired sensitivity: The sensitivity goal for each source. If a rectangle has been defined, this value should be what is desired in the final mosaic i.e. including beam overlaps. For ``Individual Pointing(s)'', it is the value per pointing, even if a custom mosaic has been defined.
- Bandwidth used for Sensitivity: Specify which bandwidth should be used to calculate the time required. This is used in conjunction with the desired sensitivity and the Representative Frequency. A number of shortcuts are possible or a user-defined value can be entered. ``RepresentativeWindowResolution'' is the usual default and will use the narrowest spectral resolution (including Hanning smoothing and spectral averaging) of the spectral window chosen as the sensitivity driver for the observations. ``FinestResolution'' refers to the smallest spectral resolution of any of the defined spectral windows. For spectral scans, FinestResolution should be chosen.
- Do you request complementary ACA observations?: Based on the user-entered values of largest angular scale, angular resolution and Representative Frequency, the OT will suggest whether the ACA is required and set the choice automatically. Changing this must be justified and is not recommended. The ACA choice will be reset if the angular resolution and largest angular scale in source change.
- Time Estimate: Request an estimate of how long it will take to achieve the scientific objectives of the Science Goal. This brings up a dialogue that contains a lot of information about the times required and parameters used in their derivation. The times reported include calibration and overheads (hardware and software) for each array required.
- Is more time required due to u,v coverage issues?: If complicated and bright sources are being observed, the sensitivity target might not be reached due to limited u,v coverage. The sensitivity-based time estimate can be overridden here, but this must be rigorously justified. The time entered must be equal to the total time required for all the arrays, including calibration and overheads. This option is probably only useful for experts and it is not expected that it will be used very much.
- Are the observations time-constrained?: Clicking this reveals a interface for setting various scheduling constraints for the observations. When specifying dates, it is important to bear in mind that anything with a scheduling margin of less than
7 days may not be possible. Time-constrained observations that require more than a single 12-m configuration are not allowed. Three options are available:
- Specific dates - multiple time windows can be entered, during one of which the SG should be executed.
- Multiple epochs - multiple dates (either absolute or relative to one of the epochs) at each of which the SG should be executed.
- Continuous monitoring - if the scientific goals are not driven by sensitivity, but rather by the need to observe a source for a fixed amount of time for monitoring purposes, the time required for this should be entered here and should be the total required for the single 12-m configuration, plus calibration and overheads. As it is expected that this will be used when the sensitivity requires less time than that for the monitoring, a validation warning will appear if this is not the case. This option is not allowed if the time has been overridden due to u,v coverage issues.
If time constrained observing is selected, it must be thoroughly justified in the Technical Justification node.
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Up: Phase 1 and Phase
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The ALMA OT Team, 2014 May 21