Placing the spotted T Tauri star LkCa 4 on an HR diagram

Abstract

Ages and masses of young stars are often estimated by comparing their luminosities and effective temperatures to pre-main sequence stellar evolution tracks, but magnetic fields and starspots complicate both the observations and evolution. To understand their influence, we study the heavily-spotted weak-lined T-Tauri star LkCa 4 by searching for spectral signatures of radiation originating from the starspot or starspot groups. We introduce a new methodology for constraining both the starspot filling factor and the spot temperature by fitting two-temperature stellar atmosphere models constructed from Phoenix synthetic spectra to a high-resolution near-IR IGRINS spectrum. Clearly discernable spectral features arise from both a hot photospheric component $T_{\mathrm{hot}}\sim 4100$ K and to a cool component $T_{\mathrm{cool}}\sim 2700-3000$ K, which covers $\sim 80\%$ of the visible surface. This mix of hot and cool emission is supported by analyses of the spectral energy distribution, rotational modulation of colors and of TiO band strengths, and features in low-resolution optical/near-IR spectroscopy. Although the revised effective temperature and luminosity make LkCa 4 appear much younger and lower mass than previous estimates from unspotted stellar evolution models, appropriate estimates will require the production and adoption of spotted evolutionary models. Biases from starspots likely afflict most fully convective young stars and contribute to uncertainties in ages and age spreads of open clusters. In some spectral regions starspots act as a featureless veiling continuum owing to high rotational broadening and heavy line-blanketing in cool star spectra. Some evidence is also found for an anti-correlation between the velocities of the warm and cool components.

Accepted to ApJ, GitHub repository available at https://github.com/BrownDwarf/welter

References in corpus (23)

• The NumPy array: a structure for efficient numerical computation
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• An Optical Spectroscopic Study of T Tauri Stars. I. Photospheric Properties
• The Magnetic Fields of Classical T Tauri Stars
• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• Probing T Tauri Accretion and Outflow with 1 Micron Spectroscopy
• Results of the ROTOR-program. I. The long-term photometric variability of classical T Tauri stars
• Results of the ROTOR-program. II. The long-term photometric variability of weak-line T Tauri stars
• A Large-Area Search for Low-Mass Objects in Upper Scorpius II: Age and Mass Distributions
• Older and Colder: The impact of starspots on pre-main sequence stellar evolution
• Empirical Tests of Pre-Main-Sequence Stellar Evolution Models with Eclipsing Binaries
• The Gaia-ESO Survey: Chromospheric Emission, Accretion Properties, and Rotation in $\gamma$ Velorum and Chamaeleon I
• Rotation, inflation, and lithium in the Pleiades
• IN-SYNC I: Homogeneous Stellar Parameters from High Resolution APOGEE Spectra for Thousands of Pre-main Sequence Star
• A Young Planet Search in Visible and IR Light: DN Tau, V836 Tau, and V827 Tau
• Modelling the magnetic activity & filtering radial velocity curves of young Suns: the weak-line T Tauri star LkCa 4
• Carbon in Red Giants in Globular Clusters and Dwarf Spheroidal Galaxies
• Stellar activity with LAMOST. I. Spot configuration in Pleiades
• The effect of starspots on the radii of low-mass pre-main sequence stars
• Sub-stellar Companions and Stellar Multiplicity in the Taurus Star-Forming Region
• The JCMT Gould Belt Survey: SCUBA-2 observations of circumstellar disks in L 1495
• Anomalous Accretion Activity and the Spotted Nature of the DQ Tau Binary System
• Testing Model Atmospheres for Young Very Low Mass Stars and Brown Dwarfs in the Infrared: Evidence for Significantly Underestimated Dust Opacities