The structure of the collapsing envelope around the low-mass protostar IRAS 16293-2422

Using H2O, OI and SiO data, we derive the structure of the collapsing envel ope around the low-mass protostar IRAS 16293-2422 down to r similar to 30 A U. With an accurate model which computes self-consistently the chemical com position, thermal balance and line emission from a collapsing envelope (Cec carelli et al. 1996), we find that IRAS 16293-2422 is a 0.8 Mo protostar ac creting from the surrounding envelope at a rate of 3.5 x 10(-5) M. yr(-1), in good agreement with previous studies. The model predicts that the water abundance in the outer (r greater than or equal to 150 AU) part of the enve lope is 5 x 10(-7) with respect to H nuclei, while it is a few times larger at smaller radii (r less than or equal to 150 AU). This enhancement result s from the evaporation of icy grain mantles when the temperature exceeds si milar to 100 K. The same model can reproduce the observations of the SiO J= 2-3 to J=8-7 lines provided the abundance of SiO is 1.5 x 10(-8) in the inn er region, while it is only 4 x 10(-12) in the rest of the envelope. The Si O abundance enhancement in the inner regions is likely due to the evaporati on of the grain mantles also responsible for the abundance enhancement of H 2O. The cooling and heating mechanisms of the gas throughout the envelope a s derived from the model are discussed, and used to derive the gas temperat ure profile.