Measuring the Spot Variability of T Tauri Stars Using Near-infrared Atomic Fe and Molecular OH Lines

• Published in: The Astrophysical journal Vol. 973; no. 2; pp. 124 - 147
• Main Authors: Tang, Shih-Yun, Johns-Krull, Christopher M., Prato, L., Stahl, Asa G.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.10.2024; IOP Publishing
• Subjects: Extrasolar planets; Gratings (spectra); Inclination angle; Infrared analysis; Infrared spectra; Infrared spectrometers; Infrared spectroscopy; Infrared stars; Line spectra; Metallicity; Near infrared radiation; Orbits; Planetary rotation; Pre-main sequence stars; Radial velocity; Stars; Starspots; Stellar effective temperatures; Stellar spectral lines; Stellar surfaces; T Tauri stars; Variability
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ad5e7f

Abstract As 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 μ m and ∼1.56362 μ m, and molecular OH at ∼1.56310 and ∼1.56317 μ m, 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.