Grain growth in the envelopes and disks of Class I protostars
We present new 3 mm ATCA data of two Class I young stellar objects (YSOs) in the Ophiucus star forming region: Elias29 and WL12. For our analysis we compare them with archival 1.1 mm SMA data. In the (u,v) plane the two sources present a similar behavior: a nearly constant non-zero emission at long baselines, which suggests the presence of an unresolved component and an increase of the fluxes at short baselines, related to the presence of an extended envelope. Our data analysis leads to unusually low values of the spectral index α_(1.1−3 mm), which may indicate that mm-sized dust grains have already formed both in the envelopes and in the disk-like structures at such early stages. To explore the possible scenarios for the interpretation of the sources we perform a radiative transfer modeling using a Monte Carlo code, in order to take into account possible deviations from the Rayleigh-Jeans and optically thin regimes. Comparison between the model outputs and the observations indicates that dust grains may form aggregates up to millimeter size already in the inner regions of the envelopes of Class I YSOs. Moreover, we conclude that the embedded disk-like structures in our two Class I YSOs are probably very compact, in particular in the case of WL12, with outer radii down to tens of AU.
© 2014 ESO. Article published by EDP Sciences Received 30 October 2013; Accepted 1 May 2014; Published online 07 July 2014. The authors wish to thank ATNF & CSIRO staff for the support and the hospitality, F. Trotta and F. Testi for their help during the observing session. The authors also thank E. van Dishoeck and the referee, J. Jørgensen, for insightful comments that significantly improved our work. This work was partly supported by the ESO DGDF program and by the Italian Ministero dell'Istruzione, Università e Ricerca through the grant Progetti Premiali 2012-iALMA.
Submitted - 1405.0821v1.pdf
Published - aa22945-13.pdf