HST FUV monitoring of TW Hya

TL;DR

This study uses HST/COS to monitor the C IV emission in TW Hya, aiming to understand the influence of accretion, winds, and stellar activity on FUV emission line profiles in young stars.

Contribution

It presents a detailed observational campaign and a model for asymmetric C IV lines, linking FUV emission features with stellar rotation, accretion, and wind processes.

Findings

C IV line profiles show asymmetry linked to stellar activity.

Correlations found between FUV emission and accretion rates.

Evidence of wind influence on emission line shapes.

Abstract

Classical T Tauri stars (CTTS) are young (< 10 Myr), cool stars that actively accrete matter from a disk. They show strong, broad and asymmetric, atomic FUV emission lines. Neither the width, nor the line profile is understood. Likely, different mechanisms influence the line profile; the best candidates are accretion, winds and stellar activity. We monitored the C IV 1548/1550 Ang doublet in the nearby, bright CTTS TW Hya with the Hubble Space Telescope Cosmic Origin Spectrograph (HST/COS) to correlate it with i) the cool wind, as seen in COS NUV Mg II line profiles, ii) the photometric period from joint ground-based monitoring, iii) the accretion rate as determined from the UV continuum, and iv) the Ha line profile from independent ground-based observations. The observations span 10 orbits distributed over a few weeks to cover the typical time scales of stellar rotation, accretion and winds. Here we describe a model with intrinsically asymmetric C IV lines.