Where are the hot ion lines in classical T Tauri stars formed?

TL;DR

This study analyzes hot ion emission lines in classical T Tauri stars to understand gas velocities and temperatures, revealing diverse line shifts and widths, and suggesting outflows as a possible origin for some emissions.

Contribution

It provides a comprehensive analysis of hot ion lines in CTTS using archival data and theoretical models, highlighting the complexity of emission mechanisms.

Findings

Line shifts range from -170 km/s to +100 km/s.

Most linewidths exceed stellar rotational broadening.

Blue-shifted lines correlate with excess X-ray absorption.

Abstract

Classical T Tauri stars show a plethora of in- and outflow signatures in a variety of wavelengths bands. In order to constrain gas velocities and temperatures we analyse the emission in the hot ion lines. We use all available archival FUSE spectra of CTTS to measure the line widths, fluxes and shifts and complement this sample with HST/GHRS and HST/STIS data. We present theoretical estimates for temperatures reached in possible emission models like jets, winds, disks and accretion funnels and look for correlations with X-ray lines and absorption properties. We find line shifts in the range from -170 km/s and +100 km/s. Most linewidths exceed the stellar rotational broadening. Those CTTS with blue-shifted lines also show excess absorption in X-rays. CTTS single out from MS stars by their large ratio of the O VII to O VI luminosities. No single emission mechanism can be found for all objects. The properties of those stars with blue-shifted lines are compatible with an origin in a shock-heated dust-depleted outflow.