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Astron. Astrophys. 349, 595-604 (1999)

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The influence of hydrogen molecules on shock-cloud collisions

A. Horváth 1 and U. Ziegler 2

1 Széchenyi István College, Department of Mathematics, Hédervári u. 3., H-9026 Gyr, and Loránd Eötvös University, Budapest, Hungary
2 Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstrasse 15, D-69121 Heidelberg, Germany

Received 18 November 1997 / Accepted 26 April 1999


The interaction of shock fronts with molecular clouds is investigated. For this purpose, a two-fluid model describing an H-[FORMULA] gas mixture is applied. The resulting equations are solved with a 2D axial-symmetric, fully compressive hydrodynamics code. Radiative cooling and the thermodynamical properties of the [FORMULA] molecule, ie. rotational and vibrational degrees of freedom as well as thermal dissociation, are taken into account.

The evolution of the shock/cloud system using this more sophisticated thermodynamical model is found to be very different from that involving a pure atomic H gas which obeys the ideal gas law. For example, the maximum density of the shocked cloud is about 5-10 times lower in the latter case. This significant result might become very important when estimating triggered star formation rates. Another difference is that in the case of H-[FORMULA] mixture, the shocked cloud gets a comet-like structure because of a smaller reexpansion.

From the numerical experiments we conclude that the application of the ideal gas law is insufficient and gives only a crude approximation of the real dynamics of a shock/cloud collision.

Key words: hydrodynamics – molecular data – methods: numerical – ISM: clouds

Send offprint requests to: András Horváth (horvatha@szif.hu)

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999