## 1.8. High Time Resolution, Pulsars, Planets and VLBI

### 1.8.1. High Time Resolution and Pulsar Observing

In pulsar binning mode, the correlator cycle time (normally 10 seconds) is divided into an integer number of pulsar periods. Each pulsar period is further divided into N equal time intervals called bins. The integration in the correlator is done separately for each bin, such that at the end of the cycle, N quantities are produced, each of which represents the integrated value at a particular pulsar phase. The minimum time bin is around 110 micro-seconds, allowing, for example, 32 phase bins for a 3.5 milli-second pulsar. The correlator will also record both the full 2 GHz continuum bands in addition to the pulsar binning data, analagous to how the zoom modes are recorded.

For high time resolution observations, a time resolution of order 10 milliseconds is possible, though with a reduced number of channels across each 2 GHz band (achieved by averaging over 1 MHz channels).

### 1.8.2. Solar System Objects

The Compact Array can track sources with non-sidereal rates, such as planets or comets. In this case delay tracking is adjusted continuously to account for source proper motion. However the pointing tracks a fixed celestial position during a scan. Thus scans must be short enough that there is not significant proper motion across the primary beam in the course of a scan. This is rarely a problem.

JPL ephemerides of the planets are built into the observing program, and a simple mechanism exists to import current JPL ephemerides of other solar system objects (e.g. new comets).

### 1.8.3. Tied Array Mode

A tied array capability is available. It provides tying of the array at one or two frequencies and, for CABB, initially at a bandwidth of 64 MHz.

The tied array adder is controlled via a process called catie which runs within cacor. This allows the choice of which antennas are included and whether the adder produces linear or circular polarisation outputs. The array is phased up in the usual way, and an option to allow the insertion of a 90° phase offset between the A and B linear polarisations at each antenna – thereby forming circular polarisation at the tied-array output – is available.

The tied-array adder can be fed into the LBA (Long Baseline Array) DAS which provides outputs for the VLBI disk-based recorders at bandwidths between 62.5 kHz and 64 MHz. Simultaneous Compact Array and tied array operation is possible, although currently this is limited to 64 MHz in both IFs, or 64 MHz in one IF and the full 2 GHz (which is not formed into a tied array) in the other.