The next two sections describe some necessary considerations for both centimetre and millimetre observations at the ATCA. This section on centimetre observations is also relevant for millimetre observers and should be read by everyone planning to propose for the ATCA. The millimetre section describes some additional requirements specific to millimetre observations.
Table 1.4. Continuum brightness temperature sensitivity (12 hr integration) for bandwidth specified in Table 1.1, for various arrays.
|16cm||0.02 K||2.1 mK||0.53 mK||0.1 mK||0.1 mK||0.02 mK|
|4cm||0.01 K||1.6 mK||0.4 mK||0.07 mK||0.11 mK||0.01 mK|
|15mm||0.02 K||2.6 mK||0.65 mK||0.12 mK||0.18 mK||0.02 mK|
|7mm||0.03 K||4.8 mK||1.2 mK||0.22 mK||0.33 mK||0.04 mK|
|3mm||—||—||—||1.4 mK||2.1 mK||0.24 mK|
It is crucial to obtain good calibration data during your observations, and you must consider how much of an overhead calibration will represent before you propose an experiment. A detailed description of the calibration required is given in Section 2.2.
The amount of calibration required will also depend on when the experiment is scheduled. Observations requiring maximum phase stability (e.g., at wavelengths less than 6cm) should be made in winter, or at night.
The general expressions for the flux and brightness sensitivities are given in the document AT/01.17/025, and these general expressions have been used in Table 1.1. The observer has control of the integration time ( ), bandwidth (B), observing wavelength ( ), number of baselines (N) and synthesized beam size ( ) only, and with these variables and the system sensitivity ( ), the expressions reduce approximately to:
where is in Jy, in min, B in MHz, in cm, and is in arcsec. For the full 6 km array, N=15. There is a convenient ATCA sensitivity calculator which takes into account system temperature, observing frequency, array, correlator configuration and (u,v)-weighting. (A pre-CABB version of the calculator is also available on the ATCA web page for use when considering the utility of archival ATCA data.)