THE PROPAGATION OF Ly Delta a IN EVOLVING PROTOPLANETARY DISKS

• Published in: The Astrophysical journal no. 2; p. jQuery1323903070786='48'
• Main Authors: Bethell, Thomas J, Bergin, Edwin A
• Format: Journal Article
• Language: English
• Published: 01.10.2011
• ISSN: 0004-637X
• DOI: 10.1088/0004-637X/739/2/78

We study the role resonant scattering plays in the transport of Ly Delta *a photons in accreting protoplanetary disk systems subject to varying degrees of dust settling. While the intrinsic stellar far-UV (FUV) spectrum of accreting T Tauri systems may already be dominated by a strong, broad Ly Delta *a line (~80% of the FUV luminosity), we find that resonant scattering further enhances the Ly Delta *a density in the deep molecular layers of the disk. Ly Delta *a is scattered downward efficiently by the photodissociated atomic hydrogen layer that exists above the molecular disk. In contrast, FUV-continuum photons pass unimpeded through the photodissociation layer and (forward-)scatter inefficiently off dust grains. Using detailed, adaptive grid Monte Carlo radiative transfer simulations we show that the resulting Ly Delta *a/FUV-continuum photon density ratio is strongly stratified; FUV-continuum-dominated in the photodissociation layer and Ly Delta *a-dominated field in the molecular disk. The enhancement is greatest in the interior of the disk (r ~ 1 AU) but is also observed in the outer disk (r ~ 100 AU). The majority of the total disk mass is shown to be increasingly Ly Delta *a dominated as dust settles toward the midplane.