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LyA Scattering in T Tauri Systems: Insights from HST’s ULLYSES Program

Presentation #406.18 in the session Young Stellar Objects and T Tauri Stars — iPoster Session.

Published onJun 29, 2022
LyA Scattering in T Tauri Systems: Insights from HST’s ULLYSES Program

T Tauri systems, the young precursors to Sun-like stars, display broad LyA emission lines that originate from their accretion shocks. The LyA photons travel through the protoplanetary disks, outflowing winds, and the ISM before reaching the observer. This produces asymmetric features, with the blue or red sides of the emission line profiles absorbed by outflowing or infalling gas. The observed ratios of red to blue LyA flux are strongly correlated with near-IR emission from small dust grains, implying some co-evolution of the accretion shocks and dust/gas disks (Arulanantham et al. 2021). We explore the impact of including resonant scattering in models fit to the observed LyA profiles from T Tauri stars, to constrain the H I column densities, intrinsic LyA widths, and gas velocities along the lines of sight. Our sample consists of targets in Data Releases 1, 2, and 3 of the Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program. For each target, we derive best-fit parameters from models with and without scattering included. While the scattering models generally fit the data better, the FWHMs and H I column densities are consistent between models. Instead, the scattering models provide more accurate estimates on the velocities of absorbing gas. We compare the best-fit velocities to other tracers of the hot inner disk regions, including near-IR veiling, forbidden line properties, and mass accretion rates.

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