Tang, Shih-YunJohns-Krull, Christopher M.Prato, L.Stahl, Asa G.2024-10-292024-10-292024Tang, S.-Y., Johns-Krull, C. M., Prato, L., & Stahl, A. G. (2024). Measuring the Spot Variability of T Tauri Stars Using Near-infrared Atomic Fe and Molecular OH Lines. The Astrophysical Journal, 973(2), 124. https://doi.org/10.3847/1538-4357/ad5e7fhttps://hdl.handle.net/1911/117958As part of the Young Exoplanets Spectroscopic Survey, this study explores the spot variability of 13 T Tauri Stars (TTSs) in the near-infrared H band, using spectra from the Immersion GRating INfrared Spectrometer. By analyzing effective temperature (T eff) sensitive lines of atomic Fe i at ∼1.56259 μm and ∼1.56362 μm, and molecular OH at ∼1.56310 and ∼1.56317 μm, we develop an empirical equivalent width ratio (EWR) relationship for T eff in the range of 3400–5000 K. This relationship allows for precise relative T eff estimates to within tens of Kelvin and demonstrates compatibility with solar metallicity target models. However, discrepancies between observational data and model predictions limit the extension of the T eff–EWR relationship to a broader parameter space. Our study reveals that both classical and weak-line TTSs can exhibit T eff variations exceeding 150 K over a span of 2 yr. The detection of a quarter-phase delay between the EWR and radial velocity phase curves in TTSs indicates spot-driven signals. A phase delay of 0.06 ± 0.13 for CI Tau, however, suggests additional dynamics, potentially caused by planetary interaction, inferred from a posited 1:1 commensurability between the rotation period and orbital period. Moreover, a positive correlation between T eff variation amplitude and stellar inclination angle supports the existence of high-latitude spots on TTSs, further enriching our understanding of stellar surface activity in young stars.engExcept where otherwise noted, this work is licensed under a Creative Commons Attribution (CC BY) license. Permission to reuse, publish, or reproduce the work beyond the terms of the license or beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Journal articleTang_2024_ApJ_973_124https://doi.org/10.3847/1538-4357/ad5e7f