1. Primary calibration of the flux scale

The standard flux density calibrator used for cm observations with ATCA (PKS1934-638) is about 0.5Jy at 30GHz and fainter still at higher frequencies. As such, the primary flux calibration at 7mm is to be done (if at all possible) on Uranus. As long as there is more than about 1Jy of flux on some baselines,Uranus should be used; use the miriad task PLPLT to plot visibility amplitudes for a given planet at a given epoch and frequency as a function of baseline.

Check the rise and set times of the planets. If Uranus is never above 30 degrees during your scheduled observations, then please contact Lisa Harvey-Smith well in advance of your observations. We are currently working on finding other sources for flux calibration at 7mm.

Absolute flux calibration at all frequencies with ATCA should now be applied using the miriad task MFBOOT. This has superceded both tasks PLBOOT and GPBOOT.

2. Secondary calibrators

A secondary calibrator must be observed intermittently during your observations. The phases of the secondary are used for taking out the atmospheric path changes and any errors in the baseline parameter determinations, as well as for correcting for the elevation dependent changes in the opacity.

The calibrators database gives information on potential sources that may be used to measure the interferometer amplitude/phase calibration. Since the 7mm is still fairly new, the information on the calibrator database is dynamic- and being improved weekly. Ideally, you would want an unresolved calibrator with a flux density greater than 1Jy at a distance no more than 5 degrees from your program source. In practice, I would first relax the the distance to 10 degrees and then the flux density to 0.5 Jy. Check the vis function and ensure that the calibrator is not resolved in your scheduled array configuration. Be skeptical but take note of the defect parameter- especially if there are measured defects at cm wavelengths.

3. Bandpass calibration

Spectral-line observers are advised to observe bandpass calibrators with every observing session/day and separately correct each days data for the bandpass complex gain before merging datasets. There seems to be some temporal variation at the upper edge of the band for the second IF in the 16MHz correlator configurations.

4. Antenna Reference Pointing

The global pointing solutions determined after every reconfiguration can be off by as much as 20 arcsec in individual antennas.

At 40 GHz, this corresponds to about 25% of the size of the primary beam. Reference pointing should therefore be implemented as part of your observing strategy for all 7mm observations. The pointing solutions should be updated about once per 90minutes or whenever you move to a different part of the sky.

Ensure that you update your pointing before observing your absolute flux density calibrator (usually a planet). Pointing on a planet is fine if it is not resolved (check in advance using plplt in miriad).