The Chemical Composition and Gas‐to‐Dust Mass Ratio of Nearby Interstellar Matter

Recent results on nearby interstellar gas and interstellar byproducts withinthe solar system are used to select among the equilibrium radiative transfermodels of the nearest interstellar material of Slavin and Frisch (2002).Assuming O/H~400 ppm, Models 2 and 8 are found to yield good fits to availabledata on local interstellar material, and pickup ions and anomalous cosmic raysinside of the heliosphere, with the exception of Ne. For these models, thedensity of interstellar gas at the entry point to the heliosphere is n(HI)~0.20/cc and n(e-)~0.1 /cc. These models suggest the chemical composition of thenearby ISM is ~60--70% subsolar if S is undepleted (where HI and HII must beincluded for abundance calculations). Gas-to-dust mass ratios of 178-183 forsolar abundances, or 611-657 for 70% solar abundances are found. The percentageof the dust mass that is carried by iron is directly correlated with thegas-to-dust mass ratio implying an Fe-rich grain core remains after graindestruction.Comment: 36 pages, 6 figures, accepted by Ap