REMNANT MOLECULAR CLOUDS IN THE ORI-OB-1 ASSOCIATION

We suggest and give some evidence that as an HII region expands and th e O stars evolve into B giants, remains of the molecular clouds first appear as bright-rimmed clouds, then as cometary globules and finally as small clouds which are visible by the reflected light from the B gi ants. We propose to call the last of these 'reflection clouds' and all three categories collectively 'remnant clouds'. A list is presented o f about 80 objects of these remnant clouds in the Ori OB 1 association . In the Belt region there is a beautiful spatial sequence from bright -rimmed clouds through cometary globules to reflection clouds. We susp ect that retarded star formation in remnant clouds can explain the pre sence of so-called dispersed T Tau stars in the peripheries of OB asso ciations.