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Abstract 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 0.45–0.6M⊙and 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 estimatingTeffandL⋆to 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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Measuring the Spot Variability of T Tauri Stars Using Near-infrared Atomic Fe and Molecular OH Lines
Abstract As part of the Young Exoplanets Spectroscopic Survey, this study explores the spot variability of 13 T Tauri Stars (TTSs) in the near-infraredHband, using spectra from the Immersion GRating INfrared Spectrometer. By analyzing effective temperature (Teff) sensitive lines of atomic Feiat ∼1.56259μm and ∼1.56362μm, and molecular OH at ∼1.56310 and ∼1.56317μm, we develop an empirical equivalent width ratio (EWR) relationship forTeffin the range of 3400–5000 K. This relationship allows for precise relativeTeffestimates 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 theTeff–EWR relationship to a broader parameter space. Our study reveals that both classical and weak-line TTSs can exhibitTeffvariations 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 betweenTeffvariation 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.
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- Award ID(s):
- 2009197
- PAR ID:
- 10544135
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 973
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 124
- Size(s):
- Article No. 124
- Sponsoring Org:
- National Science Foundation
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