VLBI observations of 10 CSO candidates: expansion velocities of hot
  spots
  Observations of ten Compact Symmetric Objects ({\rm CSO}) candidates have
been made with the Very Long Baseline Array at 8.4 GHz in 2005 and with a
combined Chinese and European VLBI array at 8.4 GHz in 2009. The 2009
observations incorporate for the first time the two new Chinese telescopes at
Miyun and Kunming for international astrophysical observations. The
observational data, in combination with archival VLBA data from previous
epochs, have been used to derive the proper motions of the VLBI components.
Because of the long time baseline of $\sim$16 years of the VLBI data sets, the
expansion velocities of the hot spots can be measured at an accuracy as high as
$\sim$1.3 $\mu$as yr$^{-1}$. Six of the ten sources are identified as CSOs with
a typical double or triple morphology on the basis of both spectral index maps
and their mirror-symmetry of proper motions of the terminal hot spots. The
compact double source J1324+4048 is also identified as a CSO candidate. Among
the three remaining sources, J1756+5748 and J2312+3847 are identified as
core-jet sources with proper motions of their jet components relating to
systemic source expansion. The third source J0017+5312 is likely also a
core-jet source, but a robust detection of a core is needed for an unambiguous
identification. The kinematic ages of the CSOs derived from proper motions
range from 300 to 2500 years. The kinematic age distribution of the CSOs
confirm an overabundance of compact young CSOs with ages less than 500 years.
CSOs with known kinematic ages may be used to study the dynamical evolution of
extragalactic radio sources at early stages.
