Sky Coverage

For detailed information about the coordinates of the ATCA see here. (Coordinate information about other Australia Telescope observatories is also included.)

The elevation limit of each antenna is 12°.

The figure below shows the azimuth-elevation diagram for the Compact Array. For a source of given declination, the contours indicate the elevation and azimuth.

Figure 3.1: Azimuth-Elevation diagram for the ATCA.

For full twelve hour synthesis, using an east-west configuration, the array is limited to sources with declinations south of around $-$25°. As well as this decrease in $uv$ coverage, more northerly objects also suffer from the problem of an increasingly elongated beam shape as the declination approaches 0° in east-west configurations. (The beam-width is greater in declination by a factor of cosec($\delta$), where $\delta$ is the source declination.)

For compact antenna configurations, such as those for mm observations, northerly sources (declinations south of around +20°) can be usefully observed with the ATCA hybrid arrays (which combine antennas on the east-west and northern arms of the array).

See here for a list of standard array configurations.

The Virtual Radio Interferometer demonstrates hour angle and visibility coverage of the available ATCA array configurations at the declination of your source. (Ensure that your browser is java enabled.) It also shows the effect of incomplete $uv$-coverage by simulating images of your virtual observation on a variety of standard source shapes. Beam sizes are listed in the table below.

You also need to consider the possibility of geometrical shadowing of one antenna by another when using baselines of 60m or less. For a 30m baseline, shadowing occurs if the antennas' azimuth is in the approximate range 60° to 120° (or 240° to 300°), and the elevation is less than 30°. The problem rapidly diminishes with increasing baseline. Shadowing decreases visibility amplitudes. See here, or http://www.narrabri.atnf.csiro.au/observing/shadowing/, for plots of shadowing limits of standard arrays.