2000A&A...355.1129C

Using H₂O, OI and SiO data, we derive the structure of the collapsing envelope around the low-mass protostar IRAS 16293-2422 down to r∼30AU. With an accurate model which computes self-consistently the chemical composition, thermal balance and line emission from a collapsing envelope (Ceccarelli et al. 1996ApJ...471..400C), we find that IRAS 16293-2422 is a 0.8M_☉ protostar accreting from the surrounding envelope at a rate of 3.5x10^–5M_☉/yr, in good agreement with previous studies. The model predicts that the water abundance in the outer (r≥150AU) part of the envelope is 5x10^–7 with respect to H nuclei, while it is a few times larger at smaller radii (r≤150AU). This enhancement results from the evaporation of icy grain mantles when the temperature exceeds ∼100K. The same model can reproduce the observations of the SiO J=2-3 to J=8-7 lines provided the abundance of SiO is 1.5x10^–8 in the inner region, while it is only 4x10^–12 in the rest of the envelope. The SiO abundance enhancement in the inner regions is likely due to the evaporation of the grain mantles also responsible for the abundance enhancement of H₂O. The cooling and heating mechanisms of the gas throughout the envelope as derived from the model are discussed, and used to derive the gas temperature profile.