Dust coagulation in dense molecular clouds: The formation of fluffy aggregates
V. Ossenkopf;
AaA, 1993, 280, 617
ABSTRACT:We set up a detailed model for the dust coagulation process in dense cores of molecular clouds without beginning star formation.
We took into
account the effects of thermal, turbulent, gravitational motion, motion from
incidential particle asymmetries, grain rotation, charges, and the accretion of
molecules onto the particles.
For the first time, we explicitly considered the
irregularity and changing fluffiness of the clusters produced in the coagulation
process.
The basis for this treatment was an independent numerical simulation of
the structure of such aggregates.
We fitted the structure parameters by
analytic functions which were used in the final model for the coagulation of the
interstellar particles.
With this model we carried out numerous simulations of the
evolution of dust grain distributions in dense cores.
Different gas densities,
clump models, accretion rates, and initial grain size distributions were
investigated.
It was found that the main force driving the aggregation of dust particles
in dense clumps is turbulence at gas densities below 108
H-atoms/cu cm and Brownian motion at higher densities.
The total opacity of the
resulting distributions of fluffy dust agglomerates was calculated using
effective-medium theories combined with a core-mantle model for the aggregate
particles.
The far infrared absorptivity is enhanced by the factor 3 (at 200
micrometers) in the first steps of the coagulation process and hardly influenced by
the further coagulation.
For gas densities between 106 and
109/cu cm and timescales below 105 yrs, the coagulation process
is efficient in changing the optical properties of the dust particles but
not in the production of large heavy particles.
KEYWORDS: agglomeration, coagulation, cosmic dust, extinction, interstellar matter, mathematical models, molecular clouds, numerical analysis, electric charge, gas dynamics, gravitation, kinematics, thermodynamic properties, turbulence effects, velocity measurement
PERSOKEY:dust, size distribution, ,
CODE: ossenkopf93