Constraints to the magnetospheric properties of T Tauri stars - II. The Mg II ultraviolet feature

TL;DR

This study analyzes Mg II ultraviolet spectral features of 44 T Tauri stars to understand their atmospheric structure, outflows, and magnetospheric interactions, revealing correlations between line broadening, flux, outflow velocity, and accretion rate.

Contribution

It provides a detailed analysis of Mg II line profiles in T Tauri stars, linking spectral features to physical properties and outflows, using archival UV data for the first time.

Findings

Warm wind absorbs blue wing of Mg II profiles

Correlation between line broadening, flux, outflow velocity, and accretion rate

Mg II flux correlates with C IV and He II fluxes

Abstract

The atmospheric structure of T Tauri Stars (TTSs) and its connection with the large scale outflow is poorly known. Neither the effect of the magnetically mediated inter- action between the star and the disc in the stellar atmosphere is well understood. The Mg II multiplet is a fundamental tracer of TTSs atmospheres and outflows, and is the strongest feature in the near-ultraviolet spectrum of TTSs. The International Ultraviolet Explorer and Hubble Space Telescope data archives provide a unique set to study the main physical compounds contributing to the line profile and to derive the properties of the line formation region. The Mg II profiles of 44 TTSs with resolution 13,000 to 30,000 are available in these archives. In this work, we use this data set to measure the main observables: flux, broadening, asymmetry, terminal velocity of the outflow, and the velocity of the Discrete Absorption Components. For some few sources repeated observations are available and variability has been studied. There is a warm wind that at sub-AU scales absorbs the blue wing of the Mg II profiles. The main result found in this work is the correlation between the line broadening, Mg II flux, terminal velocity of the flow and accretion rate. Both outflow and magnetospheric plasma contribute to the Mg II flux. The flux-flux correlation between Mg II and C IV or He II is confirmed; however, no correlation is found between the Mg II flux and the ultraviolet continuum or the H2 emission.