The nature of some doubtful open clusters as revealed by HIPPARCOS

We discuss the nature of some galactic open clusters by using proper motions and parallaxes from the Hipparcos and ACT catalogues. We show that the clusters Collinder 399, Upgren 1, NGC 1252 and Melotte 227 do not exist. Collinder 132 is found to be mainly composed out of members of an OB association, but there may be a star cluster present in this area too. Roeser & Bastian (1994) proposed that NGC 2451 consists of two star clusters. We show that NGC 2451 A definitively does exist, NGC 2451 B may exist. A star cluster may also be present in the area of Roslund 5. The Hipparcos data finally confirm the reality of Collinder 135.