EDP Sciences
Free Access
Volume 435, Number 1, May III 2005
Page(s) 177 - 182
Section Interstellar and circumstellar matter
DOI https://doi.org/10.1051/0004-6361:20042092
Published online 25 April 2005

A&A 435, 177-182 (2005)
DOI: 10.1051/0004-6361:20042092

Molecular freeze-out as a tracer of the thermal and dynamical evolution of pre- and protostellar cores

J. K. Jørgensen1, F. L. Schöier2 and E. F. van Dishoeck1

1  Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
    e-mail: jjorgensen@cfa.harvard.edu
2  Stockholm Observatory, AlbaNova, 106 91 Stockholm, Sweden

(Received 17 May 2004 / Accepted 27 January 2005 )

Radiative transfer models of multi-transition observations are used to determine molecular abundances as functions of position in pre- and protostellar cores. The data require a "drop" abundance profile with radius, with high abundances in the outermost regions probed by low excitation 3 mm lines, and much lower abundances at intermediate zones probed by higher frequency lines. The results are illustrated by detailed analysis of CO and HCO+ lines for a subset of objects. We propose a scenario in which the molecules are frozen out in a region of the envelope where the temperature is low enough ($\la$40 K) to prevent immediate desorption, but where the density is high enough (>104-105 cm-3) that the freeze-out timescales are shorter than the lifetime of the core. The size of the freeze-out zone is thereby a record of the thermal and dynamical evolution of the cores. Fits to CO data for a sample of 16 objects indicate that the size of the freeze-out zone decreases significantly between class 0 and I objects, explaining the variations in, for example, CO abundances with envelope masses. However, the corresponding timescales are $10^{5\pm 0.5}$ years, with no significant difference between class 0 and I objects. These timescales suggest that the dense pre-stellar phase with heavy depletions lasts only a short time, of the order of 105 yr, in agreement with recent chemical-dynamical models.

Key words: stars: formation -- ISM: molecules -- ISM: abundances

SIMBAD Objects

© ESO 2005

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.