3mm Home Page System Performance Calibration Observing Quick Start System Specs mmATCA Receivers mmATCA Results

1. Permitted observing frequencies

The Compact array allows simultaneous observing in two polarisations at each of two frequencies. For 3-mm observations, the centres of the two observing bands must both be in the range 85 to 105 GHz; additionally, the two frequencies are required to be at most 2.7 GHz apart and have integer MHz values.

This 2.7 GHz restriction in separation is set by the bandwidth of the current ATCA 6 and 3cm band conversion, which the 3mm receivers are fed into. This restriction will be removed with the Compact Array Broad Band upgrade (CABB) where full 8GHz separation in the two frequencies will be possible. CABB will replace the current system in March 2009.

Continuum observers who wish to image sources using the 3-mm system with the best possible sensitivity and a 2 x 128 MHz bandwidth should choose to place their band centres at frequencies 128 MHz apart at 93504 and 95552 MHz

2. Permitted observing bandwidths with the system until March 2009

Either or both frequencies can have bandwidths of 64 or 128 MHz. The first frequency can have a narrow bandwidth of 4, 8, 16 or 32 MHz. See the list of available correlator configurations in the ATCA users guide to determine the appropriate frequency to tune the ATCA receiver.

To know what the bandwidth and channel resolution are for a particular observing frequency use the ATCA sensitivity calculator .

3. Field of View

The FWHM of the antenna primary beam is 36 arcsec at 86 GHz.

4. Polarisation

Polarisation measurements are currently not possible with the ATCA 3mm system.

5. Array Configuration / Synthesised Beam

Observations with compact, and preferably hybrid, array configurations are optimum for detection or sensitivity-limited experiments at 12mm, 7mm and 3mm. This is because:

• Atmospheric phase fluctuations lead to decorrelation of visibilities which worsens with increasing observing frequency and baseline length.




• Low spatial resolution will optimise the potential for the emission to be unresolved and thus maximise the signal-to-noise ratio.




• Higher air mass at low elevations leads to higher system temperatures. There is a dramatic increase in the system temperature at elevations below 30 degrees. Full synthesis is obtained in 6 hours for a hybrid array. This reduces the need to observe at low elevations in many cases.

To know what the synthesised beam is for a particular array configuration use the ATCA sensitivity calculator.

Note that only 5 antennas are equipped with the 3mm receiver package. Antenna 6 on the 6km is the antenna left out. In most cases observations at 3mm using the 750X, 1.5X or 6X arrays will be severely hampered by atmospheric phase noise. Observers are discouraged from using such arrays without first getting data using the more compact arrays configurations.