Kevin France (CASA/University of Colorado) 

Far-Ultraviolet H2 Emission: 
Interstellar and Circumstellar Media

Molecular hydrogen (H2) is important in almost all astrophysical
environments, from the early universe to the interstellar medium to
star and planet formation.  I will discuss recent studies of molecular
hydrogen emission in the interstellar medium and in the circumstellar
environments of stars at both ends of their life cycles.  I will give
an overview of the observational signatures of H2 in these
environments and focus on outstanding questions that can be addressed
by spectroscopic studies at far-UV wavelengths.  I will briefly
discuss the space-based instruments that have been used to perform
such observations, predominantly FUSE and sounding rocket payloads.  I
will then show results from photodissociation regions (PDRs), where we
study the relative contributions of H2 and dust at the interface
between molecular clouds and strong UV radiation fields.  These data
have been used to test improved models of H2 fluorescence. I will
discuss the models and what additional physical processes may be
important for future fluorescence codes.  Finally, I will discuss
recent results on circumstellar media at different stages of stellar
evolution, from the recent discovery of H2 in a gas-poor
protoplanetary disk to constraints on the molecular excitation
mechanisms in planetary nebula outflows.