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. 
Edward D. Young
astro-ph.EP astro-ph.SR