Dust Grain Size Distributions from MRN to MEM

Employing the Maximum Entropy Method algorithm, we fit interstellarextinction measurements which span the wavelength range 0.125-3 micron. Wepresent a uniform set of MEM model fits, all using the same grain materials,optical constants and abundance constraints. In addition, we are takingadvantage of improved UV and IR data and better estimates of the gas-to-dustratio. The model fits cover the entire range of extinction properties that havebeen seen in the Galaxy and the Magellanic Clouds. The grain models employedfor this presentation are the simplistic homogeneous spheres models (i.e.,Mathis, Rumpl, & Nordsieck 1977) with two (graphite, silicate) or three(graphite, silicate, amorphous carbon) components. Though such usage is only afirst step, the results do provide interesting insight into the use of grainsize as a diagnostic of dust environment. We find that the SMC Bar extinctioncurve cannot be fit using carbon grains alone. This is a challenge to therecent observational result indicating little silicon depletion in the SMC.Comment: 24 pages, 5 figures, accepted for publication in the Astrophysical Journa