  Data from a recent Australia Telescope Compact Array (ATCA) program of
multi-frequency, multi-epoch monitoring of 202 active galactic nuclei with
declinations < +10 degrees have been searched for GHz Peaked Spectrum (GPS) and
Compact Steep Spectrum (CSS) radio sources. Supplementary data at higher and
lower frequencies, where available, have been used to further examine the
spectral properties of previously reported and new candidate GPS and CSS
sources. The ATCA monitoring program has allowed the variability and
polarization properties of sources previously reported as GPS and CSS sources,
and the majority of new GPS and CSS candidates, to be investigated, confirming
that these are useful diagnostics in discriminating genuine GPS and CSS sources
from variable sources that display similar spectra only temporarily. GPS
sources are confirmed to be generally more compact, and less polarized, than
CSS sources, although CSS sources show evidence for being somewhat less
variable than GPS sources at 1.4 and 2.5GHz. In addition, the widths of GPS
spectra are examined, and a significant difference is found in the GPS sample
of Snellen et al. (2000) between sources with compact double (CD) or compact
symmetric object (CSO) morphologies and sources with other morphologies, in
that CD and CSO sources have generally narrower spectra. Possible reasons for
this difference are considered.

Astrophysics