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

T Tauri systems, the young precursors to Sun-like stars, produce broad LyA emission lines (FWHM = 500-700 km/s). The LyA photons are generated at the accretion shocks and must travel through an outflowing wind, protoplanetary disk, and the ISM before reaching the observer. This produces asymmetric features, with the blue or red sides absorbed by outflowing or infalling H I. The ratios of red to blue flux are correlated with properties of the protoplanetary disks, indicating that disk and wind evolution are linked (Arulanantham et al. 2021). By fitting accurate models to the LyA emission lines, we can quantify the kinematics at the intersection between the inner disks, wind launching regions, and accretion flows.