Hostname: page-component-78c5997874-fbnjt Total loading time: 0 Render date: 2024-11-14T06:50:21.307Z Has data issue: false hasContentIssue false
  • English
  • Français

Thermal processes in molecular gas

Published online by Cambridge University Press:  03 August 2017

J.P. Chièze  and
C. de Boisanger
J.P. Chièze
Affiliation:
Commissariat à l'Energie Atomique, Centre d'Etudes de Bruyères-le-Châtel, Service PTN, 91680 Bruyères-le-Châtel, France
C. de Boisanger
Affiliation:
Commissariat à l'Energie Atomique, Centre d'Etudes de Bruyères-le-Châtel, Service PTN, 91680 Bruyères-le-Châtel, France

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The dynamics of the cold atomic and molecular gas, on which we focus here, is strongly affected by non equilibrium heating and cooling processes. We give two different examples, in which the breaking of the thermal balance is due respectively to variations of the incident ultraviolet radiation flux, and non equilibrium abundances of H 2 molecules in molecular clouds envelopes. Fluctuations of the ultraviolet radiation flux in clumpy molecular cloud envelopes result in the formation or the destruction of dense regions. Large density contrasts, greater than one order of magnitude, are easily achieved in cloud regions of moderate visual extinction. Condensation or expansion develop on quite short time scales, of the order of a few tenth of million year, and induce collective motions which can feed turbulence.

Another example of the importance of out of equilibrium thermochemical processes is furnished by the study of the H — H 2 transition layers in molecular clouds envelopes. They turn out to be unstable against convection-like motions, driven by the energy released by H 2 photodestruction. The gas velocities involved in these motions are, again, typical of the observed turbulent velocity in clouds envelopes.

Keywords

Interstellar mediumclouds – Interstellar mediumkinematics and dynamics of – Interstellar mediumthermal processes
Type
Shocks and Instabilities
Information
Symposium - International Astronomical Union , Volume 147: Fragmentation of Molecular Clouds and Star Formation , 1991 , pp. 197 - 204
Copyright
Copyright © Kluwer 1991 

References

Balbus, S.A.: 1986, Astrophys. J., 303, L79 Google Scholar
Balbus, S.A.: 1988, Astrophys. J., 328, 395 Google Scholar
Balbus, S.A. and Soker, N.: 1989, Astrophys. J., 341, 611 Google Scholar
Black, J.: 1987, in Interstellar Processes, eds Hollenbach, and Thronson, , Reidel Publishing Company, p. 731.Google Scholar
de Boisanger, C. and Chièze, J.P.: 1991, Astron. Astrophys. (in press) Google Scholar
Boissé, P.: 1990, Astron. Astrophys. 228, 483.Google Scholar
Chièze, J.P., Pineau des Forêts, G.: 1987, Astron. Astrophys. 183, 98.Google Scholar
Chièze, J.P., Pineau des Forêts, G.: 1989, Astron. Astrophys. 221, 89.Google Scholar
Chièze, J.P., Pineau des Forêts, G., Herbst, E.: 1991, Astrophys. J. (in press) Google Scholar
Elitzur, M., Watson, W.D.: 1978, Astron. Astrophys. 70, 443.Google Scholar
Field, G.B., Goldsmith, D.W., Habing, H.J.: 1969, Astrophys. J. Letters 155, 149.Google Scholar
Graff, M.M.: 1989, Astrophys. J. 339, 289.Google Scholar
Hattori, M., and Habe, A.: 1990, Monthly Notices Roy. Astron. Soc. 242, 399.Google Scholar
Heck, L., Flower, D.R., Pineau des Forêts, G.: 1990, Comp. Phys. Comm. 58, 169.Google Scholar
d'Hendecourt, L.B., and Léger, A.: 1987, Astron. Astrophys. 180, L9.Google Scholar
de Jong, T., Dalgarno, A., Boland, W.: 1980, Astron. Astrophys. 91, 68.Google Scholar
Lepp, S. and Dalgarno, A.: 1988, Astrophys. J. 324, 553.Google Scholar
Mathis, J.S., Mezger, P.G., Panagia, N.: 1983, Astron. Astrophys. 128, 212.Google Scholar
Meyer, J.P.: 1989, in Cosmic Abundance of Matter, ed Waddington, C.J., AIP Conference Proceedings 183, The American Institute of Physics, New York, p. 245.Google Scholar
Pineau des Forêts, G., Flower, D.R., Dalgarno, A.: 1988, Monthly Notices Roy. Astron. Soc. 235, 621.Google Scholar
Puget, J.L. and Léger, A.: 1989, Ann. Rev. Astron. Astrophys. 27, 161.Google Scholar
Savage, B.D., Bohlin, R.C., Drake, J.F., Budich, W.: 1977, Astrophys. J. 216, 291.Google Scholar
Stutzki, J., Stacey, G.J., Genzel, R., Harris, A.I., Jaffe, D.T., Lugten, J.B.: 1988, Astrophys. J. 332, 379.Google Scholar
Williams, D.A.: 1987, in Physical Processes in Interstellar Clouds, eds Morfill, and Scholer, , Reidel Publishing Company, p. 377.Google Scholar