Revised Depletions and New Constraints on Interstellar Dust Composition

We have reviewed the literature on composition of young stars, both hot and cool, as well as older solar-type stars. We find that all these classes of stars have lower abundances of the heavy elements (specifically C, N, O, Mg, Si, and Fe) than the sun. Therefore studies of interstellar depletions in which the solar composition is used as the reference standard are probably in error, tending to overestimate the total quantities of these elements, hence the depletions. We have revised the depletion estimates, using stellar abundances as the reference standard and making use of recent IS gas-phase abundance measurements. As a result of our revised depletions, we can place new and stringent constraints on several published models for the interstellar dust.