2006ApJS..165..256H

We survey fluorescent H₂emission in HST STIS spectra of the classical T Tauri stars (CTTSs) TW Hya, DF Tau, RU Lupi, T Tau, and DG Tau, and the weak-lined T Tauri star (WTTS) V836 Tau. From each of those sources we detect between 41 and 209 narrow H₂emission lines, most of which are pumped by strong Lyα emission. H₂emission is not detected from the WTTS V410 Tau. The fluorescent H₂emission appears to be common to circumstellar environments around all CTTSs, but high spectral and spatial resolution STIS observations reveal diverse phenomenon. Blueshifted H₂emission detected from RU Lupi, T Tau, and DG Tau is consistent with an origin in an outflow. The H₂emission from TW Hya, DF Tau, and V836 Tau is centered at the radial velocity of the star and is consistent with an origin in a warm disk surface. The H₂lines from RU Lupi, DF Tau, and T Tau also have excess blueshifted H₂emission that extends to as much as -100 km/s. The strength of this blueshifted component from DF Tau and T Tau depends on the upper level of the transition. In all cases, the small aperture and attenuation of H₂emission by stellar winds restricts the H₂emission to be formed close to the star. In the observation of RU Lupi, the Lyα emission and the H₂emission that is blueshifted by 15 km/s are extended to the SW by ∼0".07, although the faster H₂gas that extends to ∼100 km/s is not spatially extended. We also find a small reservoir of H₂emission from TW Hya and DF Tau consistent with an excitation temperature of ∼2.5x10⁴ K.