1977 • 6 materials – Graphite – Silicon carbide, SiC, Enstatite (Fe,Mg)SiO 3, Olivine (Fe,Mg) 2 SiO 4 – Iron, Magnetite Fe 3 O 4 • Grain shapes: spheres and infinite cylinders • Fit size distribution n(a) as 18 discrete bins from 0 to 1 micron • Constrained by UV/optical extinction and C, Si, Mg, Fe abundances • All fits require C, no strong constraints on the other material (only two components required by data) • Discuss polarization
silicates – Later work: graphite and modified astronomical silicate • Grain shapes: spheres – Later work: oblate and prolate spheriods w/ a range of axial ratios • Fit mass distributions as 60 discrete bins – Use Maximum Entropy Method • Constrained by extinction, abundances, & (later work) polarization – consistent w/ scattering and IR emission)
graphite, 3 types of amorphous carbon – Silicates – Composites of silicates, organics, water ice, and voids • Grain shapes: spheres • Fit size distributions with discrete bins w/ regularization (smoothness) – Provide analytical fits to resulting distributions • Constrained by extinction, abundances, and IR emission • All models investigated fit the constraints used – additional constraints needed
mantle – Very small carbonaceous particles – PAHs • Grain shapes: spheres and finite cylinders • Fit exponential size distributions • Constrained by UV-MIR extinction, polarization, and C, Si, Mg, Fe, O, & N abundances
grains coated with carbonaceous material – PAH (molecules) – Very small grains of amorphous carbon • Grain shapes • Fit to powerlaw size distributions • Constrained by extinction & emission • Introduces “astronomical PAHs”
of dust grains – Bigger/smaller grains, new materials, ... • Quantitatively compare different grain materials – Bayesian statistics may help (Bayes Factors) • Add additional observational constraints – E.g., albedo and scattering phase function asymmetry
graphite” based on heterogeneous lab data • 2 components • Grain shapes: spheres • Test MRN powerlaw size distributions • Constrained by extinction & emission
– Silicates • Grain shapes: spheres • Fit mass distributions as 60 discrete bins (MEM) • Constrained by extinction & abundances • Fit MW, LMC, SMC and individual sightlines