The radio source OQ 208: Parsec-scale morphology and spectral properties

We present results from global VLBI (Very Long Baseline Interferometry) observations at 5 GHz of the radio source OQ 208. The milliarcsecond (mas) morphologoy of the radio emission is described by an asymmetric compact double structure with a flux density ratio between the two components of about 10:1, and a projected total size of similar to 7 mas (i.e. similar to 7 pc). Both components are resolved by the present observations. Multifrequency VLA (Very Large Array) observations are used to define the spectral shape and, together with literature data, to investigate the flux density variability at different frequencies. The integrated radio spectrum is peaked at about 4 GHz. The flux density is constant below the peak and slowly decreasing at frequencies above the peak. On the basis of the mas morphology, spectral information and flux density variations, we favour the hypothesis that the radio source consists of two parsec-size lobes undergoing synchrotron radiative losses.