The Effects of UV Continuum and Lyman alpha Radiation on the Chemical Equilibrium of T Tauri Disks

Abstract

We show in this Letter that the spectral details of the FUV radiation fields have a large impact on the chemistry of protoplanetary disks surrounding T Tauri stars. We show that the strength of a realistic stellar FUV field is significantly lower than typically assumed in chemical calculations and that the radiation field is dominated by strong line emission, most notably Lyman alpha radiation. The effects of the strong Lyman alpha emission on the chemical equilibrium in protoplanetary disks has previously been unrecognized. We discuss the impact of this radiation on molecular observations in the context of a radiative transfer model that includes both direct attenuation and scattering. In particular, Lyman alpha radiation will directly dissociate water vapor and may contribute to the observed enhancements of CN/HCN in disks.

14 pages, 4 figures, accepted by ApJ Letters

References in corpus (7)

• Accretion Disks Around Young Objects. III. Grain Growth
• Warm Molecular Layers in Protoplanetary Disks
• The FUV spectrum of TW Hya. I. Observations of H${}_2$ Fluorescence
• Submillimeter lines from circumstellar disks around pre-main sequence stars
• Axi-symmetric models of ultraviolet radiative transfer with applications to circumstellar disk chemistry
• Two-dimensional Distributions and Column Densities of Gaseous Molecules in Protoplanetary Disks II
• Observations of T-Tauri Stars using HST-GHRS: I. Far Ultraviolet Emission Lines

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