SIMBAD references

A new realization of the International Celestial Reference System (ICRS) is built upon the data of the HIPPARCOS catalogue and astrometric ground-based catalogues of the 20^th century reduced to the HIPPARCOS system. Non-linear motion of some stars has been detected with this realization of the ICRS. This motion is separated into the proper motion of the barycentre and the revolution of the photocentre around the barycentre. The latter is believed to be induced by fainter components of star-like mass. The periodic motion of the photocentres of the stellar systems HIP 4427 (γ Cas), HIP 11072, HIP 45699, HIP 54214 and HIP 116727 is discussed in detail. Related periods and amplitudes are evaluated and proposed for confirmation by other methods. The periodic motion of the photocentre of Be star γ Cas is of particular interest.