Protostars and Planets VI, Heidelberg, July 15-20, 2013
Ultraviolet Molecular Emission from T Tauri Stars: H2, CO, and the Lyman-alpha Radiation Field
France, Kevin (Colorado)
Schindhelm, Eric (SwRI)
Herczeg, Gregory (KIAA/Peking University)
The composition and spatial distribution of molecular gas in the inner few AU of young (< 10 Myr) circumstellar disks are important components to our understanding of the formation and evolution of planetary systems. We present results from a far-ultraviolet (far-UV) spectroscopic survey of H2 and CO emission in protoplanetary disks. Using the new and refurbished spectrographs onboard the Hubble Space Telescope, we observe tens to hundreds of photo-excited molecular emission lines in every gas-rich disk spectrum, independent of the evolutionary state of the dust disk. All transitional disks in our sample display prominent H2 emission lines arising from a remnant, inner gas disk. Molecular line-widths and excitation temperatures suggest that the emitting H2 is concentrated between ~ 0.1 – 3 AU, while the CO fluorescence originates between 2 – 10 AU. The UV H2 emission appears to trace similar disk radii as M-band CO measurements, but the UV- and IR-emitting CO populations appear to be spatially separate. We use these data to reconstruct the local Lyman-alpha radiation field, finding that Lyman-alpha dominates the far-UV energy budget in all cases.
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