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Fluorescent molecular hydrogen in the Eagle nebula L. E. Allen,* M. G. Burton, S. D. Ryder, M. C. B. Ashley and J. W. V. Storey
 

Summary: Fluorescent molecular hydrogen in the Eagle nebula
L. E. Allen,* M. G. Burton, S. D. Ryder,▓ M. C. B. Ashley and J. W. V. Storey
School of Physics, University of New South Wales, Sydney 2052, Australia
Accepted 1998 November 11. Received 1998 November 6; in original form 1998 March 25
A B S T R AC T
We used the University of New South Wales Infrared Fabry-Perot (UNSWIRF) to
investigate the photodissociation region (PDR) associated with the `elephant trunk'
features in the M16 H ii region (the Eagle nebula). Images were made in the H2 1▒0
S(1) and 2▒1 S(1) lines at 2.122 and 2.248 mm, respectively, and in the H i Br g line at
2.166 mm. The trunk-like features have an average H2 number density of ,104
cm└3
and
are irradiated by a far-UV «eld ,104
┤ the ambient interstellar value. The H2 intensity
pro«le across the trunks is consistent with a simple model in which cylindrical columns of
gas are illuminated externally, primarily by a direct component (the stars of NGC 6611),
with an additional contribution from an isotropic component (scattered light). We «nd that
most of the H2 emission from the source is consistent with purely »uorescent excitation,
however a signi«cant fraction of the H2 emission (,25 per cent) from the northernmost
column shows evidence for `collisional »uorescence', i.e. redistribution of H2 level

  

Source: Ashley, Michael C. B. - School of Physics, University of New South Wales

 

Collections: Physics