ASTRONOMICAL OXYGEN ISOTOPIC EVIDENCE FOR SUPERNOVA ENRICHMENT OF THE SOLAR SYSTEM BIRTH ENVIRONMENT BY PROPAGATING STAR FORMATION

New infrared absorption measurements of oxygen isotope ratios in CO gas from individual young stellar objects confirm that the solar system is anomalously high in its [O-18]/[O-17] ratio compared with extrasolar oxygen in the Galaxy. We show that this difference in oxygen isotope ratios is best explained by similar to 1% enrichment of the protosolar molecular cloud by ejecta from Type II supernovae from a cluster having of order a few hundred stars that predated the Sun by at least 10-20 Myr. The likely source of exogenous oxygen was the explosion of one or more B stars during a process of propagating star formation.