VLBI monitoring of the structure of the ICRF sources - The Bordeaux VLBI Image Database

The extragalactic radio sources that make up the International Celestial Reference Frame (ICRF) can exhibit extended and time-variable brightness distributions (or structures) on VLBI scales, setting limits on the accuracy of the astrometric source positions determined from VLBI. For this reason, regular VLBI observations are organized to image and monitor these structures. The primary observations used for this purpose are the so-called ``Research \& Development with the VLBA" (RDV) sessions, initiated almost three decades ago. Systematic imaging of the sources observed in these sessions is carried out by the Bordeaux group with the goal of tracking the structural evolution of the ICRF sources on the long-term. The VLBI images produced along with metrics that characterize the source structure are made available to the scientific community via the Bordeaux VLBI Image Database (BVID). Occasionally, other sessions, either at higher radio frequencies, i.e. K band (24 GHz) and Q band (43 GHz), or from other observing programs, are also used for imaging, At present, the database includes more than 8000 VLBI images for more than 1500 sources, with up to 50+ epochs per source. The available data may be used for astrometric and astrophysical research, like selecting the defining sources for the ICRF, modeling source structure in astrometric and geodetic VLBI, and studying the nature and evolution of the sources. The BVID is accessible at the following url: https://bvid.astrophy.u-bordeaux.fr