5 Discussion

The VLBA observations have produced images with sufficient resolution to describe the source morphology for the large majority of cases.

The present observations do not allow to pick up the radio core, due to the relatively low observing frequency, but the overall morphology strongly indicates that the sources are mostly two-sided. We see either well separated lobes or lobes connected by bridges, possibly jets. Most sources are edge brightened, suggesting the presence of hot spots, in general not fully resolved from the mini-lobe emission, which contribute most of the source flux density. We tentatively classify these sources as CSOs (two of them are actually MSOs). There are also a few objects with edge darkening, as B3 2304+377, B3 2348+450 and B3 2358+406. There are a number of sources where a compact component, centrally located, could be the source core. However, having only one relatively low frequency we are not in the position to make a definitive statement about core identifications.

Some asymmetries in the flux densities of the two sides are seen, as also some moderate distortions. B3 0800+472 and B3 2304+377 are extreme examples. The sources B3 1225+442 and B3 1449+421 are reminiscent of an S morphology (see also Stanghellini et al. 2001).

The average ratio between the component size transverse to the source axis ( $\theta_{\rm trans}$) and Largest Angular Size (LAS) is $\theta_{\rm trans}/LAS \sim 0.08 \pm 0.02$, consistent with findings in other source samples (e.g. Fanti et al. 1990).

We have computed the equipartition parameters for the source components, under the following assumptions: a) proton to electron energy ratio of one; b) filling factor of one; c) maximum and minimum electron (and proton) energies corresponding to synchrotron emission in the frequency range 100 GHz to 10 MHz; d) ellipsoidal volumes with axis corresponding to the observed ones. We also computed the brightness temperatures ($T_{\rm B}$) of each component. In order to make easier the reading of the paper, we do not report the individual component values, since they can be obtained from the parameters in Table 2, but only mention the typical values.

The magnetic fields are in the range of several mGauss, going up to $\sim$20 mGauss in the most compact components (e.g. B3 1133+432). Brightness temperatures range from $\sim$10⁸ up to $\leq$10¹¹ K.