Evolution of the pc-scale structure of PKS 1934-638 revisited: first
  science with the ASKAP and New Zealand telescopes
  We have studied the archetypal Gigahertz Peaked Spectrum radio galaxy, PKS
1934-638, using the Australian Long Baseline Array, augmented with two new
telescopes that greatly improve the angular resolution of the array. These VLBI
observations represent the first scientific results from a new antenna in NZ
and the first antenna of the Australian SKA Pathfinder (ASKAP). A compact
double radio source, PKS 1934-638, has been monitored over a period of 40
years, and the observation described here provides the latest datum, eight
years after the previous observation, to aid in the study of the long-term
evolution of the source structure. We take advantage of these new long
baselines to probe PKS 1934-638 at the relatively low frequency of 1.4 GHz, in
order to examine the effects of optical depth on the structure of the radio
source. Optical depth effects, resulting in the observation of frequency
dependent structure, may have previously been interpreted in terms of an
expansion of the source as a function of time. Expansion and frequency
dependent effects are important to disentangle in order to estimate the age of
PKS 1934-638. We show that frequency dependent structure effects are likely to
be important in PKS 1934-638 and present a simple two-dimensional synchrotron
source model in which opacity effects due to synchrotron self-absorption are
taken into account. Evidence for expansion of the radio source over 40 years is
therefore weak, with consequences for the estimated age of the radio source.
