Grain growth in the envelopes and disks of Class I protostars ^⋆

¹ European Southern Observatory (ESO), Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
e-mail: miotello@mpe.mpg.de
² Università degli Studi di Milano, Dipartimento di Fisica, via Celoria 16, 20133 Milano, Italy
³ INAF – Osservatorio Astrofidico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany
⁵ Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena CA 91125, USA
⁶ Max-Planck-institute für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
⁷ Australia Telescope National Facility, PO Box 76, NSW 1710 Epping, Australia
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA
⁹ School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, 2 Dublin, Ireland

Received: 30 October 2013
Accepted: 1 May 2014

Abstract

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.