%APérez Paolino, Facundo%ABary, Jeffrey%APetersen, Michael%AWard-Duong, Kimberly%ATofflemire, Benjamin%AFollette, Katherine%AMach, Heidi%BJournal Name: The Astrophysical Journal; Journal Volume: 946; Journal Issue: 1; Related Information: CHORUS Timestamp: 2024-01-16 12:32:32 %D2023%IDOI PREFIX: 10.3847 %JJournal Name: The Astrophysical Journal; Journal Volume: 946; Journal Issue: 1; Related Information: CHORUS Timestamp: 2024-01-16 12:32:32 %K %MOSTI ID: 10402697 %PMedium: X; Size: Article No. 10 %TCorrelating Changes in Spot Filling Factors with Stellar Rotation: The Case of LkCa 4 %XAbstract

We present a multi-epoch spectroscopic study of LkCa 4, a heavily spotted non-accreting T Tauri star. Using SpeX at NASA’s Infrared Telescope Facility (IRTF), 12 spectra were collected over five consecutive nights, spanning ≈1.5 stellar rotations. Using the IRTF SpeX Spectral Library, we constructed empirical composite models of spotted stars by combining a warmer (photosphere) standard star spectrum with a cooler (spot) standard weighted by the spot filling factor,fspot. The best-fit models spanned two photospheric component temperatures,Tphot= 4100 K (K7V) and 4400 K (K5V), and one spot component temperature,Tspot= 3060 K (M5V) with anAVof 0.3. We find values offspotto vary between 0.77 and 0.94 with an average uncertainty of ∼0.04. The variability offspotis periodic and correlates with its 3.374 day rotational period. Using a mean value forfmeanspotto represent the total spot coverage, we calculated spot corrected values forTeffandL. Placing these values alongside evolutionary models developed for heavily spotted young stars, we infer mass and age ranges of 0.45–0.6Mand 0.50–1.25 Myr, respectively. These inferred values represent a twofold increase in the mass and a twofold decrease in the age as compared to standard evolutionary models. Such a result highlights the need for constraining the contributions of cool and warm regions of young stellar atmospheres when estimatingTeffandLto infer masses and ages as well as the necessity for models to account for the effects of these regions on the early evolution of low-mass stars.

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