Interferometer Setup

The physical setup of antennas onto stations is the responsibility of the operators and technical team. The astronomical setup of the interferometer involves a number of steps that are done under the joint responsibility of the array operator and on-duty IRAM astronomer. These include:

• Antenna Pointing: after a configuration change, the ``minor'' antenna pointing parameters (Azimuth axis inclinations and encoder zeros) must be redetermined. The operator makes the necessary observations and reduces the data using a standard procedure, with help from the on-duty astronomer if required. Both operator and on-duty astronomer must agree on the results before setting up the new parameters. Major pointing parameters (e.g. collimations) are monitored on longer time intervals (1 to 2 months) during dedicated test time, and should only be changed if approved by the IRAM astronomer responsible for antenna pointing.
• Delay measurements: the zero delay (cable length difference after geometric path length compensation) is measured by the operator using a standard procedure.
• Baseline measurements: the accuracy of positioning an antenna on a station is of the order of 2 mm, insufficient for precise phase tracking. Actual baseline lengths are measured to a fraction of a mm by observations of point sources of known positions. As with antenna pointing, these observations and the associated data reduction are done by the operator and the result must be approved by the on-duty astronomer.
• Receiver tuning is done by the operator. The performance of the receiver (T_sys and image gain ratio) must be checked by the operator and on-duty astronomer before starting scientific observations.
• Focussing is also a joint responsibility of the operator and on-duty astronomer.

Only after all this setup is the array ready for astronomical observations.