Short-Term Variability of Accreting T-Tauri Stars using TESS Light Curves

Classical T Tauri stars are young, low-mass stars that gain mass through the highly variable process of magnetospheric accretion. Simulations of the region where accreted material collides with the stellar chromosphere, known as the accretion shock, predict a thermal instability that may act as one possible source of variability. The predicted periodic behavior ranges from hundredths of a second to an hour, depending on the assumed cooling function, density, accretion stream velocity and metallicity of the accretion shock. Previous attempts to study this short-term behavior have been limited by either their observational cadence or duration and have not established a clear sense of whether these instabilities are observable. We report month-long, two-minute cadence light curves from TESS of 14 T-Tauri stars to perform a comprehensive study of their short-term quasi-periodic behavior. We computed a 2D dynamic power spectrum by applying a sliding window which allowed us to rule-out and identify specific instances of quasi-periodicity. We quantify significance by using Bayesian red noise fits and MCMC methods to derive p-values that distinguish between quasi-periodic oscillations and expected variance in periodogram windows. An absence of quasi-periodicity may suggest that current models are incomplete and in need of additional physics or that the process is happening in a non-observable location or timescale. Conversely, identifying quasi-periodic events and their characteristic timescale will further validate these models and suggest factors that may affect their observational visibility. Our research adds to the current understanding of the driving forces of T-Tauri variability and the dynamic structure of the accretion shock.