Free access article

A&A 413, 1-5 (2004)
DOI: 10.1051/0004-6361:20031505

Grain photoelectric ionisation rates, heating rates, and charge as functions of visual extinction

J. G. L. Rae¹, T. W. Hartquist¹, S. H. Lepp², P. T. O'Neill³ and D. A. Williams<sup>3

1</sup>  Department of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²  Department of Physics, University of Nevada Las Vegas, 4505 Maryland Parkway, Box 454004, Las Vegas, Nevada 89154-4004, USA
³  Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

(Received 16 May 2003 / Accepted 22 August 2003)

Abstract
Recombination onto grain surfaces is important in determining the fractional ionisation and the depletions of elements. The recombination rates of ions depend on the grain charges. We calculate the dependence of the grain charge distribution function on visual extinction for each of a number of cloud models in order to obtain the mean grain charge as a function of visual extinction. We give simple fits to the dependences on grain charge and visual extinction of photoionisation and photoelectric heating rates which may be used in the modelling of photon dominated regions.

Key words: astrochemistry -- ISM: dust, extinction

Offprint request: J. G. L. Rae, jglr@ast.leeds.ac.uk

© ESO 2004

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