Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-09-24
IAU Symposium No. 197 (2000), "Astrochemistry: From Molecular Clouds to Planetary Systems", Minh & van Dishoeck, eds., ASP, p.
Astronomy and Astrophysics
Astrophysics
11 pages, 8 figures, uses newpasp.sty
Scientific paper
Photodissociation regions (PDRs) and shocks give rise to conspicuous emission from rotationally and vibrationally excited molecular hydrogen. This line emission has now been studied with ISO and from the ground in great detail. A remarkable discovery has been that toward the Orion outflow and other shock-excited regions, the H_2 level populations show a very high excitation component. We suggest that these high-excitation populations may arise from non-thermal pumping processes, such as H_2 formation and high-velocity ion-molecule collision in partially dissociative shocks. In PDRs such as NGC 7023 however, formation pumping is always less important than fluorescent pumping. We furthermore present two HD emission line detections toward Orion Peak 1. This enables the first comparison of the H_2 and the HD excitation, which surprisingly turn out to be identical.
Bertoldi Frank
Draine Bruce T.
Drapatz Siegfried
Feuchtgruber Helmut
Geballe Theodore
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