Solid hydrogen coated graphite particles in the interstellar medium-I

Abstract

Solid hydrogen coated graphite particles may be expelled from regions of star-formation into the general interstellar medium. The solid para-hydrogen mantles, which contain a small proportion of ortho-H₂ could be stable against evaporation in the general interstellar radiation field. They are also stable against physical and chemical sputtering in H 1 regions. Extinction efficiencies are calculated for solid hydrogen particles and for graphite particles with solid hydrogen mantles. Graphite core-solid hydrogen grains are capable of producing excellent agreement with the interstellar extinction observations from 20 000-1100 Å. The graphite core radius may be in the range γ₀ = 0.04-0.06 µ and the solid hydrogen mantle radius in the range γ = 0.15-0.25µ. The albedo and phase function of these particles are consistent with the requirements imposed by[the diffuse galactic light.