PLANETS AND STARS

The basic conditions for the formation and detection of planetary syst ems around nearby stars are analyzed. About one-third of main sequence stars with masses below 10 M. can have (and probably do have, accordi ng to the most recent observations) planetary systems. As expected, al l planets discovered so far are located beyond the boundaries of the d ust evaporation zones around their central stars, but inside the outer boundaries of the zones in which planets form by accretion over the l ifetime of the central star. The central star of a planetary system ca n be not only a main sequence star, but also a white dwarf, neutron st ar, or black hole. It is not excluded that the individual components o f wide binaries, and also close binary systems, can have planetary sys tems.