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Lyα Scattering Models Trace Accretion and Outflow Kinematics in T Tauri Systems

N. Arulanantham, M. Gronke, E. Fiorellino, J. F. Gameiro, A. Frasca, J. Green, S. Chang, R. A. B. Claes, C. C. Espaillat, K. France, G. J. Herczeg, C. F. Manara, L. Venuti, P. Ábrahám, R. Alexander, J. Bouvier, J. Campbell-White, J. Eislöffel, W. J. Fischer, Á. Kóspál, M. Vioque

T Tauri stars produce broad Lyα emission lines that contribute ∼88% of the total UV flux incident on the inner circumstellar disks. Lyα photons are generated at the accretion shocks and in the protostellar chromospheres and must travel through accretion flows, winds, and jets, the protoplanetary disks, and the interstellar medium before reaching the observer. This trajectory produces asymmetric, double-peaked features that carry kinematic and opacity signatures of the disk environments. To understand the link between the evolution of Lyα emission lines and the disks themselves, we model HST-COS spectra from targets included in Data Release 3 of the Hubble UV Legacy Library of Young Stars as Essential Standards program. We find that resonant scattering in a simple spherical expanding shell is able to reproduce the high-velocity emission line wings, providing estimates of the average velocities within the bulk intervening H i. The model velocities are significantly correlated with the K-band veiling, indicating a turnover from Lyα profiles absorbed by outflowing winds to emission lines suppressed by accretion flows as the hot inner disk is depleted. Just 30% of targets in our sample have profiles with redshifted absorption from accretion flows, many of which have resolved dust gaps. At this stage, Lyα photons may no longer intersect with disk winds along the path to the observer. Our results point to a significant evolution of Lyα irradiation within the gas disks over time, which may lead to chemical differences that are observable with ALMA and JWST.

Classical T Tauri stars; Protoplanetary disks; Hubble Space Telescope; Stellar accretion; Stellar winds

Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

The Astrophysical Journal
Volume 944, Number 2
2023 February

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia