SIMBAD references

Early radio positions for a sample of 100 Hipparcos stars, three Tycho-only stars, and nine radio stars with optical positions referred to the Hipparcos/ICRS frame are analyzed. The optical proper motions are used to compare the optical and radio positions. From an original sample of 247 radio positions for the above 112 stars, a set of 220 shows coincidence between the optical and radio centers of emission closer than 500 mas. This set is analyzed for systematic departures between the optical and radio positions. A smaller subset of 136 early radio positions for 72 stars show radio-minus-optical offsets smaller than 100 mas and are useful for monitoring of the spin of the Hipparcos frame.