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

The influence of hydrogen molecules on shock-cloud collisions

A. Horváth ¹ and U. Ziegler <sup>2

1</sup> 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

Abstract

The interaction of shock fronts with molecular clouds is investigated. For this purpose, a two-fluid model describing an H- 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 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- 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)

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. The thermodynamical model
  • 2.1. The equations of dynamical evolution
  • 2.2. The energy density
  • 2.3. The equation of state
  • 2.4. The cooling function
  • 2.5. The source terms
• 3. The numerical model
  • 3.1. The cooling routine
• 4. Results
  • 4.1. The influence of dissociational processes
  • 4.2. Convergence test
  • 4.3. A series of models with different Mach-numbers
  • 4.4. A series of models with different central densities
• 5. A qualititative comparision with observations
• 6. Conclusions
• References

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999
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