Variations on solar condensation: Sources of interstellar dust nuclei

Abstract

Some portion of the interstellar dust entering the heliosphere is a refractory (Ca-Al-Ti-Mg-Si-Fe-Ni-Cr-Co-rich) component either condensed at high temperature from stellar outflows or formed in the interstellar medium (ISM). Condensation sequences for T>1100 K, assuming chemical equilibrium, are calculated for stellar outflow gas having (1) solar composition at various Ptot; (2) compositions approaching C/O=0.9, otherwise solar; (3) metallicities reduced by Z/Zo=0.10; and (4) metallicities enhanced by added dust components. Calculated depletions are relatively insensitive to these excursions from the canonical "cosmic" abundances. The intragroup similarities of depletions observed for the element groups (Ca-Ti), (Fe-Ni-Cr-Co), and (Mg-Si) reflect the dominant mineralogy calculated for stardust: Ti- and Ca-aluminate phases, metal alloy, and Mg2SiO4 (Mg-olivine). This result suggests that the bulk of the refractory component of ISM dust was condensed in stellar environments. Copyright 2000 by the American Geophysical Union.