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The structure of the collapsing envelope around the low-mass protostar IRAS 16293-2422 *
C. Ceccarelli 1,
A. Castets 2,
E. Caux 3,
D. Hollenbach 4,
L. Loinard 5,
S. Molinari 6 and
A.G.G.M. Tielens 7
Received 6 December 1999 / Accepted 21 January 2000
Using H2O, OI and SiO data, we derive the structure of the collapsing envelope around the low-mass protostar IRAS16293-2422 down to AU. With an accurate model which computes self-consistently the chemical composition, thermal balance and line emission from a collapsing envelope (Ceccarelli et al. 1996), we find that IRAS16293-2422 is a 0.8 protostar accreting from the surrounding envelope at a rate of yr-1, in good agreement with previous studies. The model predicts that the water abundance in the outer (r 150 AU) part of the envelope is with respect to H nuclei, while it is a few times larger at smaller radii (r 150 AU). This enhancement results from the evaporation of icy grain mantles when the temperature exceeds 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 in the inner region, while it is only 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.
Key words: stars: circumstellar matter stars: formation ISM: individual objects: IRAS 16293-2422
* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.
Send offprint requests to: Cecilia Ceccarelli; LAOG; (Cecilia.Ceccarelli@obs.ujf-grenoble.fr)
Online publication: March 21, 2000