Systematic analysis of spectral energy distributions and the dust opacity indices for Class 0 young stellar objects

Abstract

We are motivated by the recent measurements of dust opacity indices beta around young stellar objects (YSOs), which suggest that efficient grain growth may have occurred earlier than the Class I stage. The present work makes use of abundant archival interferometric observations at submillimeter,millimeter, and centimeter wavelength bands to examine grain growth signatures in the dense inner regions (<1000 AU) of nine Class 0 YSOs. A systematic data analysis is performed to derive dust temperatures, optical depths, and dust opacity indices based on single-component modified black body fittings to the spectral energy distributions (SEDs). The fitted dust opacity indices (beta) are in a wide range of 0.3 to 2.0 when single-component SED fitting is adopted. Four out of the nine observed sources show beta lower than 1.7, the typical value of the interstellar dust. Low dust opacity index (or spectral index) values may be explained by the effect of dust grain growth, which makes beta<1.7. Alternatively, the very small observed values of beta may be interpreted by the presence of deeply embedded hot inner disks, which only significantly contribute to the observed fluxes at long wavelength bands. This possibility can be tested by the higher angular resolution imaging observations of ALMA, or more detailed sampling of SEDs in the millimeter and centimeter bands. The beta values of the remaining five sources are close to or consistent with 1.7, indicating that grain growth would start to significantly reduce the values of beta no earlier than the late-Class 0 stage for these YSOs.