Grain Growth and Density Distribution of the Youngest Protostellar Systems

We present dust opacity spectral indexes (β) of the youngest protostellar systems (so-called Class 0 sources), L1448 IRS 2, L1448 IRS 3, and L1157, obtained between the λ = 1.3 mm and 2.7 mm continua, using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The unprecedented compact configuration and image fidelity of CARMA allow a better detection of the dust continuum emission from Class 0 sources, with a less serious missing flux problem normally associated with interferometry. Through visibility-modeling at both λ = 1.3 mm and 2.7 mm simultaneously, as well as imageand visibility-comparison, we show that β of the three Class 0 sources are around or smaller than 1, indicating that dust grains have already significantly grown at the Class 0 stage. In addition, we find a radial dependence of β, which implies faster grain growth in the denser central regions and/or dust segregation. Density distributions of the Class 0 sources are also addressed by visibility-modeling. Subject headings: circumstellar matter — stars: individual (L1448 IRS 2, L1448 IRS 3, L1157)