Radio source structure and VLBI position instabilities

Astrometric positions of extragalactic radio sources derived from VLBI data are used to build highly-accurate reference frames such as the International Celestial Reference Frame. Despite their distant locations, instabilities in the position of these sources are often seen on time scales of months to years, which is generally thought to be caused by source structure evolution. In this paper, we compare position instabilities and structural evolution for a sample of 68 sources observed over a 10-year period (1994--2003). Our results indicate that the two phenomena are linked at some level although the correlation is not perfect.