Vol. 567
In section 6. Interstellar and circumstellar matter

Grain growth in the envelopes and disks of Class I protostars

The authors present new 3 mm ATCA data of two Class I young stellar objects, Elias29 and WL12, which are expected to be surrounded by both an extended envelope and a disk. In the (u, v) plane the two sources present a similar behavior. First, there is a nearly constant emission at long baselines, which suggests the presence of an unresolved component. Second, the fluxes increase at short baselines, indicating the presence of an extended envelope. Our data analysis leads to unusually low values of the spectral index, which indicates that mm-sized dust grains have already formed at this early stage both in the envelopes and in the central, compact disk-like structures. This result may provide new constraints for the initial dust evolution in protoplanetary disks.