Correlating Changes in Spot Filling Factors with Stellar Rotation: The Case of LkCa 4. (arXiv:2303.01574v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Paolino_F/0/1/0/all/0/1">Facundo P&#xe9;rez Paolino</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bary_J/0/1/0/all/0/1">Jeffrey S. Bary</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Petersen_M/0/1/0/all/0/1">Michael S. Petersen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ward_Duong_K/0/1/0/all/0/1">Kimberly Ward-Duong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tofflemire_B/0/1/0/all/0/1">Benjamin M. Tofflemire</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Follette_K/0/1/0/all/0/1">Katherine B. Follette</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mach_H/0/1/0/all/0/1">Heidi Mach</a>

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
$approx$ 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, $f_{spot}$. The best-fit models spanned two
photospheric component temperatures, $T_{phot}$ = 4100 K (K7V) and 4400 K
(K5V), and one spot component temperature, $T_{spot}$ = 3060 K (M5V) with an
$A_V$ of 0.3. We find values of $f_{spot}$ to vary between 0.77 and 0.94 with
an average uncertainty of $sim$0.04. The variability of $f_{spot}$ is periodic
and correlates with its 3.374 day rotational period. Using a mean value for
$f^{mean}_{spot}$ to represent the total spot coverage, we calculated spot
corrected values for $T_{eff}$ and $L_star$. Placing these values alongside
evolutionary models developed for heavily spotted young stars, we infer mass
and age ranges of 0.45-0.6 $M_odot$ 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 estimating $T_{eff}$ and $L_star$ 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.

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
$approx$ 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, $f_{spot}$. The best-fit models spanned two
photospheric component temperatures, $T_{phot}$ = 4100 K (K7V) and 4400 K
(K5V), and one spot component temperature, $T_{spot}$ = 3060 K (M5V) with an
$A_V$ of 0.3. We find values of $f_{spot}$ to vary between 0.77 and 0.94 with
an average uncertainty of $sim$0.04. The variability of $f_{spot}$ is periodic
and correlates with its 3.374 day rotational period. Using a mean value for
$f^{mean}_{spot}$ to represent the total spot coverage, we calculated spot
corrected values for $T_{eff}$ and $L_star$. Placing these values alongside
evolutionary models developed for heavily spotted young stars, we infer mass
and age ranges of 0.45-0.6 $M_odot$ 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 estimating $T_{eff}$ and $L_star$ 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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