Star-disk interactions in the strongly accreting T Tauri Star S CrA N

TL;DR

This study investigates the magnetic field topology and accretion-ejection phenomena of the strongly accreting T Tauri star S CrA N using spectropolarimetry and interferometry, revealing complex magnetic structures and the need for multi-technique observations.

Contribution

It provides the first detailed magnetic field map of S CrA N and combines spectropolarimetry with interferometry to study its innermost regions.

Findings

Reconstructed a complex magnetic field topology for S CrA N.

Identified inconsistencies between magnetic field signatures and emission line data.

Highlighted the variability of the system on approximately one-day timescales.

Abstract

Aims : We aimed at constraining the accretion-ejection phenomena around the strongly-accreting Northern component of the S CrA young binary system (S CrA N) by deriving its magnetic field topology and its magnetospheric properties, and by detecting ejection signatures, if any. Methods : We led a two-week observing campaign on S CrA N with the ESPaDOnS optical spectropolarimeter at the Canada-France-Hawaii Telescope. We recorded 12 Stokes I and V spectra over 14 nights. We computed the corresponding Least-Square Deconvolution (LSD) profiles of the photospheric lines and performed Zeeman-Doppler Imaging (ZDI). We analysed the kinematics of noticeable emission lines, namely He I $\lambda 5876$ and the four first lines of the Balmer series, known to trace the accretion process. Conclusions : The findings from spectropolarimetry are complementary to those provided by optical long-baseline interferometry, allowing us to construct a coherent view of the innermost regions of a young, strongly accreting star. Yet, the strong and complex magnetic field reconstructed for S CrA N is inconsistent with the observed magnetic signatures of the emission lines associated to the post-shock region. We recommend a multi-technique, synchronized campaign of several days to put more constrains on a system that varies on a $\sim$ 1 day timescale.