PAHs in circumstellar envelopes
I. Processes affecting PAH formation and growth
T. Allain 1, 2,
E. Sedlmayr 2 and
S. Leach 1
Received 24 May 1996 / Accepted 17 September 1996
Analytical expressions are presented to estimate the interactions of gas particles with polycyclic aromatic hydrocarbons (PAHs) described as large flat plates. This modelization enables us to determine the collision rate of gas particles with PAHs, the drag force of gas particles on PAHs and the energy exchanged between PAHs and gas particles.
These results are applied to the case of the circumstellar envelopes of C-stars where PAHs are considered to form and grow. As a result of these calculations, the drift velocities of PAHs are estimated and found to be negligible in comparison with the gas thermal velocity. The determination of PAH temperatures in the envelope is also carried out. Finally, the results are discussed in the context of the role of PAHs in the formation of dust particles.
Key words: ISM: molecules molecular processes stars: circumstellar matter stars: carbon rich
Send offprint requests to: S. Leach
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998