New Insights: the Accretion Process and Variable Wind from TW Hya

TL;DR

This study captures the first detailed sequence of accretion events in a classical T Tauri star, linking X-ray, optical, and coronal responses to provide new insights into the accretion process and stellar wind dynamics.

Contribution

It introduces a comprehensive model of accretion and wind processes in young stars, based on multi-wavelength observations of TW Hya, revealing the sequence of accretion shock, downflow, and coronal heating.

Findings

First direct observation of an accretion event in a T Tauri star.

Sequential response of optical, X-ray, and coronal emissions to accretion.

Evidence that accretion heats the stellar corona and influences wind re-establishment.

Abstract

For the first time in a classical T Tauri star, we are able to trace an accretion event signaled by an hour-long enhancement of X-rays from the accretion shock and revealed through substantial sequential changes in optical emission line profiles. Downflowing turbulent material appears in H-alpha and H-beta emission. He D3 (5876 Angstrom) broadens, coupled with an increase in flux. Two hours after the X-ray accretion event, the optical veiling increases due to continuum emission from the hot splashdown region. The response of the stellar coronal emission to the heated photosphere follows about 2.4 hours later, giving direct evidence that the stellar corona is heated in part by accretion. Then, the stellar wind becomes re-established. A model that incorporates the dynamics of this sequential series of events includes: an accretion shock, a cooling downflow in a supersonically turbulent region, followed by photospheric and later, coronal heating. This model naturally explains the presence of broad optical and ultraviolet lines, and affects the mass accretion rates currently determined from emission line profiles. These results, coupled with the large heated coronal region revealed from X-ray diagnostics, suggest that current models are not adequate to explain the accretion process in young stars.