Observations of T Tauri stars using the Hubble space telescope GHRS. II. Optical and near-ultraviolet lines.
ARDILA D.R., BASRI G., WALTER F.M., VALENTI J.A. and JOHNS-KRULL C.M.
Abstract (from CDS):
We have analyzed GHRS data of eight classical T Tauri stars (CTTSs) and one weak T Tauri star (WTTS). The GHRS data consist of a spectral range 40 Å wide centered on 2800 Å. For four of the CTTSs, we have nearly simultaneous optical observations that contain Hα, Hβ, He I, Na D, and the Ca II infrared triplet. The Mg II resonance doublet is the strongest feature in the 2800 Å range. This line has a fairly wide and symmetric emission component (∼200-300 km.s–1 for the CTTSs), with a narrow central absorption and a wide blueshifted absorption superimposed to it. The narrow central absorption width and equivalent width are inconsistent with being due only to interstellar medium clouds described in the literature, which leads us to conclude that it is partially due to non-LTE processes in the emission-line region itself. The emission profile closely follows Hα. Its large width in CTTSs cannot be due to the Stark effect, and we suggest that it is due to supersonic turbulence. All the stars show blueshifted absorptions that are evidence of outflows (terminal velocities ∼300 km.s–1), with multiple flows observed in two stars. We show evidence that the wind is not spherical, with wind signatures being stronger for lower inclinations at a given accretion rate. We briefly compare other optical lines with the hot transition region lines observed in CTTS.