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S. Lacour, V. Ziskin (Institut d'Astrophysique de Paris), N. Balakrishnan (University of Nevada Las Vegas), B. Rachford (University of Colorado), P. Sonnentrucker, C. Oliveira (Johns Hopkins University), M. André, G. Hébrard, R. Ferlet, A. Vidal-Madjar (Institut d'Astrophysique de Paris)
We present a study of the high rotational bands (J > 2) of H2 toward 4 early type galactic stars. In each case, the velocity dispersion - characterized by the spectrum fitting parameter b - increases with the level of excitation. The amplitude of the line broadening, which can be as high as 10 km\,s-1, makes explanations such as inhomogeneous spatial distribution, or the presence of warm interstellar gas, unlikely. We propose a solution in which the broadening is due to those molecules that are rotationally excited through the excess energy acquired after their formation on a grain - H2-formation pumping. These same molecules carry away part of that residual energy in kinetic form which gives rise to the dispersion. We constructed a time-dependent model in which we follow the stochastic evolution of the molecules in each species, and show that the different dispersions are a natural consequence of an equilibrium among the various excitation and decay processes.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.