Inheritance of solar short- and long-lived radionuclides from molecular clouds and the unexceptional nature of the solar system

Apparent excesses in early-solar $^{26}$Al, $^{36}$Cl, $^{41}$Ca, and $^{60}$Fe disappear if one accounts for ejecta from massive-star winds concentrated into dense phases of the ISM in star-forming regions. The removal of apparent excesses is evident when wind yields from Wolf-Rayet stars are included in the plot of radionuclide abundances vs. mean life. The resulting trend indicates that the solar radionuclides were inherited from parental molecular clouds with a characteristic residence time of 10$^8$ years. This residence time is of the same order as the present-day timescale for conversion of molecular cloud material into stars. The concentrations of these extinct isotopes in the early solar system need not signify injection from unusual proximal stellar sources, but instead are well explained by normal concentrations in average star-forming clouds. The results imply that the efficiency of capture is greater for stellar winds than for supernova ejecta proximal to star-forming regions.

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 18O/17O ratio compared with extra-solar oxygen in the Galaxy. We show that this difference in oxygen isotope ratios is best explained by 1 per cent enrichment of the proto-solar 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 to 20 Myr. The likely source of exogenous oxygen was the explosion of one or more B stars during a process of propagating star formation.