Magnetic topologies of two weak-line T Tauri stars TAP 4 and TAP 40

TL;DR

This study uses Zeeman-Doppler imaging to map magnetic fields of two weak-line T Tauri stars, revealing dominant toroidal fields and surface features, and assesses their activity-induced radial velocity jitters to evaluate exoplanet detection prospects.

Contribution

First detailed magnetic topology maps of TAP 4 and TAP 40 using Zeeman-Doppler imaging, showing dominant toroidal fields and differential rotation, advancing understanding of magnetic structures in young stars.

Findings

Both stars have mainly toroidal magnetic fields (~60%)

TAP 4 exhibits large polar cool spots and intermediate warm spots

Filtered radial velocities suggest no close-in massive exoplanets

Abstract

We present a Zeeman-Doppler imaging study of two weak-line T Tauri stars TAP 4 and TAP 40, based on the high-resolution spectropolarimetric observations with ESPaDOnS at the Canada-France-Hawaii Telescope in November 2013, in the framework of the MaTYSSE large programme. We apply two Zeeman-Doppler imaging codes to the Stokes I and V profiles to reconstruct their brightness and large-scale magnetic field images. The results given by the two imaging codes are in good agreement with each other. TAP 4 shows a large polar cool spot and several intermediate-latitude warm spots on its surface, whereas TAP 40 exhibits very weak variations in its Stokes I profiles suggesting a mostly unspotted photosphere. We detect Zeeman signatures in the Stokes V profiles of both stars. The reconstructed magnetic maps reveal dominantly toroidal fields, which enclose about 60 per cent of the total magnetic energy for both of TAP 4 and TAP 40. Both stars show prominent circular ring features of the azimuthal magnetic field. We derive a solar-like surface differential rotation on TAP 4 from the tomographic modelling. The brightness image of TAP 4 is used to predict the radial velocity jitters induced by its activity. After filtering out the activity jitter, the RMS of its RVs is reduced from 1.7 km s$^{-1}$ to 0.2 km s$^{-1}$, but we do not detect any periodic signals in the filtered RVs of TAP 4, implying that it is unlikely to host a close-in exoplanet more massive than $\sim$3.5 M$_{\rm Jup}$ at 0.1 au.