FUV irradiated disk atmospheres: LYα and the origin of hot H{sub 2} emission
- Astronomy Department, 501 Campbell Hall, University of California, Berkeley, CA 94720 (United States)
Protoplanetary disks are strongly irradiated by a stellar FUV spectrum that is dominated by Lyα photons. We investigate the impact of stellar Lyα irradiation on the terrestrial planet region of disks (≲1 AU) using an updated thermal-chemical model of a disk atmosphere irradiated by stellar FUV and X-rays. The radiative transfer of Lyα is implemented in a simple approach that includes scattering by H i and absorption by molecules and dust. Because of their non-radial propagation path, scattered Lyα photons deposit their energy deeper in the disk atmosphere than the radially propagating FUV continuum photons. We find that Lyα has a significant impact on the thermal structure of the atmosphere. Photochemical heating produced by scattered Lyα photons interacting with water vapor and OH leads to a layer of hot (1500–2500 K) molecular gas. The temperature in the layer is high enough to thermally excite the H{sub 2} to vibrational levels from which they can be fluoresced by Lyα to produce UV fluorescent H{sub 2} emission. The resulting atmospheric structure may help explain the origin of UV fluorescent H{sub 2} that is commonly observed from classical T Tauri stars.
- OSTI ID:
- 22887110
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 817; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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