A New Astrophysical Interpretation of the Si and Ti Isotopic   Compositions of Mainstream SiC Grains from Primitive Meteorites
  Mainstream presolar SiC grains from primitive meteorites show a clear s-process signature in the isotopic composition of heavy trace elements. These grains most likely condensed in the winds of a variety of AGB stars. However, the non-solar and correlated Si and Ti isotopic compositions measured in these grains are inconsistent with a pure s-signature. We present a possible solution to this much-discussed problem by assuming a spread in the original composition of parent AGB stars due to small chemical inhomogeneities in the interstellar medium at the time of their birth. These inhomogeneities may naturally arise from variations in the contributions of each nuclide to the interstellar medium by the relevant stellar nucleosynthetic sites, SNII and different subtypes of SNIa. 
Maria Lugaro, Roberto Gallino, Maurizio Busso, Sachiko Amari, Ernst   Zinner