SIMBAD references

VLA astrometric positions of the radio emission from 52 stars are reported, from observations obtained between 1978 and 1995. The positions of these stars have been obtained and reduced in a uniform manner. Based on our measurements, the offset of the optical (Hipparcos) frame from the radio reference frame is in agreement with the Hipparcos extragalactic link results, within their mean errors. Comparison of the VLA measurements with the Hipparcos optical positions confirms earlier estimates of the accuracy of these positions as 30 mas. Long-term measurements of UX Ari have improved its proper motion.