SIMBAD references

Based on a preliminary reference catalogue, constructed by combining the catalogues PPM, ACRS and those of Eichhorn et al. (1970), Jones (1973) and Hertzsprung (1947), 33 exposures on 11 plates taken with the Zô-sè 40 cm refractor (f = 6895 mm) over 86 years are reduced by the central overlap technique and high-precision positions and proper motions of 441 stars in the Pleiades astrometric standard region are obtained. All the star positions have standard errors below ±0.05″ and nearly 90% of the proper motions have standard errors below ±0.001″/yr.