Rio survey of optical astrometric positions for 300 ICRF2 sources and the current optical/radio frame link status before Gaia

Abstract

We obtained improved optical positions for 300 ICRF2 sources-the Rio survey. We compared the Rio survey with 10 other selected optical astrometric surveys and studied the link between the Hipparcos Catalogue Reference Frame (HCRF) and the International Celestial Reference Frame, Second Realization (ICRF2). We investigated the possible causes for the observed non-coincidence between the optical and ICRF2 positions. The Rio survey positions were referred to the second version of the United StatesNaval Observatory CCD Astrograph Catalog (UCAC2), currently the best tested HCRF densification. The sources are between-90°