The circumstellar environment of the young, low-mass dipper star JH 223. Accretion and large-scale magnetic field topology

TL;DR

This study investigates the magnetic field topology and accretion processes of the very-low-mass, fully convective T Tauri star JH 223, revealing a predominantly poloidal magnetic field and star-disk interactions causing observable light curve dips.

Contribution

First detailed characterization of magnetic topology and accretion in a fully convective, very-low-mass T Tauri star using multi-technique observations.

Findings

Magnetic field is predominantly poloidal with a 250 G dipolar component.

Disk truncation radius is near the corotation radius, influencing accretion.

Star's rotation causes periodic obscuration, producing dipper light curves.

Abstract

Studies of magnetospheric accretion and magnetic field topology in T Tauri stars have advanced over the years, but their applications to fully convective, very-low-mass T Tauri stars remain relatively unexplored. We aim to analyze the circumstellar environment of the very-low-mass dipper-like star JH 223 by investigating the accretion process and characterizing its large-scale magnetic field topology. We analyzed the photometric variability of JH 223 using observations from multiple telescopes, including K2, TESS, and LCOGT. Additionally, we used Gemini/GRACES spectroscopic and CFHT/SPIRou spectropolarimetric data to investigate the star-disk interaction and characterize the large-scale stellar magnetic field using Zeeman-Doppler imaging. JH 223 is a fully convective classical T Tauri star with an age of about 3 Myr and a mass of 0.4 M$_{\odot}$. The large-scale surface magnetic field is predominantly poloidal, with a 250 G dipolar component. The dipole field strength and mass accretion rate indicate that the disk truncation radius is near the corotation radius. The star-disk interaction, combined with the inclined dipole, generates accretion columns that warp the inner disk. As the star rotates, this warp periodically obscures the stellar surface every 3.31 days, producing dipper light curves. The same period is also detected in radial velocity and longitudinal magnetic field variability. The accretion columns, traced by redshifted absorption in H$\alpha$ and He I 1083 nm, are associated with the inner disk warp at the same rotational phase. The accretion process in JH 223 is dynamic, transitioning from an unstable to a stable regime over a few weeks, consistent with magnetohydrodynamic simulations of star-disk interaction. Results from multi-technique observations suggest that the magnetospheric accretion model remains valid for fully convective very-low-mass young stars.