Issue |
A&A
Volume 448, Number 2, March III 2006
|
|
---|---|---|
Page(s) | 425 - 432 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361:20053837 | |
Published online | 24 February 2006 |
Determining the cosmic ray ionization rate in dynamically evolving clouds
Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK e-mail: cjl@star.ucl.ac.uk
Received:
15
July
2005
Accepted:
1
November
2005
The ionization fraction is an important factor in determining the chemical and
physical evolution of star forming regions. In the dense, dark starless cores
of such objects, the ionization rate is dominated by cosmic rays; it is
therefore possible to use simple analytic estimators, based on the relative
abundances of different molecular tracers, to determine the cosmic ray
ionization rate. This paper uses a simple model to investigate the accuracy of two well-known
estimators in dynamically evolving molecular clouds.
It is found that, although the analytical formulae based on the abundances of ,
, CO, O,
and
give a reasonably accurate
measure of the cosmic ray ionization rate in static, quiescent clouds,
significant discrepancies occur in rapidly evolving (collapsing) clouds.
As recent evidence suggests that molecular clouds may consist of complex,
dynamically evolving sub-structure, we conclude that simple abundance ratios
do not provide reliable estimates of the cosmic ray ionization rate in
dynamically active regions.
Key words: astrochemistry / stars: formation
© ESO, 2006
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