Context: Classical T Tauri stars (hereafter CTTS) show a plethora of in- and outflow signatures in a variety of wavelength bands.
Aims: In order to constrain gas velocities and temperatures, we analyse the emission in the hot ion lines.
Methods: We use all available archival FUSE spectra of CTTS to measure the widths, fluxes and shifts of the detected hot ion lines and complement these data with HST/GHRS and HST/STIS data. We present theoretical estimates of the temperatures reached in possible emission models such as jets, winds, disks and accretion funnels and look for correlations with X-ray lines and absorption properties.
Results: We find line shifts in the range from -170 km s-1 to +100 km s-1. Most linewidths exceed the stellar rotational broadening. Those CTTS with blue-shifted lines also show excess absorption in X-rays. CTTS can be distinguished from main sequence (hereafter MS) stars by their large ratio of the O VII to O VI luminosities.
Conclusions: 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.